E book 5: Renewable energy

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ENERGY Energy is the capacity to do work. A plenty of energy is needed to sustain industrial growth and agricultural production.

CLASSIFICATION OF ENERGY It is broadly classified into: 1. Conventional energy: is in practice for long duration of time and well established technology is available to tap and use them. e.g. Coal, oil, natural gas, hydro power, nuclear power etc.

2. Non-conventional energy: source can be used with advantage for power generation as well as other applications in a large number of locations and situations. These energy sources cannot be easily stored and used conveniently. e.g. Solar, wind, tidal and geothermal etc.

Based upon nature, energy sources are classified as: 1. Renewable energy sources are inexhaustible and are renewed by nature itself. Solar, wind, tidal, hydro and biomass are few examples.

2. Non-renewable energy sources are exhaustible within a definite period of time depending upon its usage. Fossil fuels (coal, oil, gas) and nuclear fuels are few examples.

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SOLAR ENERGY SYSTEM Solar energy is the light and radiant heat from the Sun that control Earth's climate and weather and protract life. It is a renewable source of energy and originates with the thermonuclear process that transfers about 650,000,000 tons of hydrogen to helium per second. This action produces lots of heat and electromagnetic radiation. The produced heat remains in the sun and is helpful in upholding the thermonuclear reaction and electromagnetic radiation together with visible, infrared and ultra-violet radiation flow out into space in all directions. Solar energy is in reality nuclear energy. Similar to all stars, the sun is a large gas sphere made up mostly of hydrogen and helium gas. In the internal surface of sun 25% of hydrogen is fusing into helium at a rate of about 7 × 1011 kg of hydrogen per second.

Heat from the center is first and foremost spread out, and then sends down, to the Sun surface, where it keeps up at a temperature of 5800 K. According to Stefan-Boltzmann’s Law, the total energy that is released by the Sun, and therefore, the quantity of solar energy that we get here on Earth, is significantly reliant upon this surface temperature. Now a day’s solar energy system play an important role in the field of producing electricity or other domestic uses like water heating, cooking etc. As we know that major part of generated electricity or electricity depends upon coal which is used in thermal power plant (in India 65% of total power is generated by the thermal power plant).

But the main problem is here that the fuel used in thermal power plant is coal which is in limited amount and may be not available in future to produce or generate electricity. That is the main reason to solar energy system comes to the picture.

Solar energy system is the pollution free source of energy and always available because, sun is the single source of solar energy (also known as renewable energy or non conventional energy) which sits at the central point of solar system and radiate energy at an tremendously huge and fairly constant rate, per day per year as the form of electromagnetic radiation. Sun contained huge amount of energy but the whole energy not utilized at earth due to some reason like:  

Earth is revolve at about its polar axis.

Atmospheric reason of earth.

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Earth is relocate from the sun.

But the main thing is that after these obstacles sun energy reach to earth is sufficient to produce or generate electricity which is polluted free. Due to this consideration somewhat we reduce the use of Thermal Power Plant, Gas Power Plant etc. and reserve the non-renewable energy sources like coal, petroleum etc. for future. In recent years solar energy system is rise as a primary source of energy that converted into electricity and almost all country in the world utilize maximum solar energy to produce electricity and this is very less costly.

The main benefit of solar energy system is that the sun light is present everywhere free of cost. To produce electricity or convert solar energy to other form of energy first we invest heavy amount for solar panel that convert solar energy to other form but the main advantage is after that installation no any type of maintenance is required for 40 to 50 years.

History of Solar Energy First solar collector created by Swiss scientist named Horace-Benedict de Saussure in 1767 he take an insulated box enclosed with three layers of glass which suck up heat energy. After that Saussure’s box became famous and widely known as the first solar oven, getting temperatures of 230 degrees Fahrenheit. After that in 1839 a most important landmark in the progression of solar energy occurs with the significant of the photovoltaic effect by a French scientist Edmond Becquerel. In this he used two electrodes placed in an electrolyte and then exposing it to the light and results is tremendous electricity increased a lot. After that lots of experiment are occurred by various scientists at time to time and modified our solar energy system to produce more electricity from solar energy. But now a day’s also in this field various experiments are doing by a scientist, how to utilize maximum solar energy which is available on the earth.

In 1873, Willoughby Smith discovered photoconductivity of a material known as selenium. In 1887 there was the discovery of the ultraviolet ray capacity to cause a spark jump between two electrodes and this was done by Heinrich Hertz. In 1891 the first solar heater was created. In 1893 the first solar cell was introduced. In 1908 William J. Baileys invented a copper collector which was constructed using copper coils and boxes. In 1958, solar energy was used in space. In the 1970′s, Exxon Corporation designed an efficient solar panel which was less costly to manufacture.

Less cost manufacturing process of solar panel became the major milestone in the history of solar energy. In 1977 the US government embraced the use of solar energy by launching the Solar Energy Research Institute. In 1981, Paul Macready produced the first solar powered aircraft. in the year 1982 there was the development of the first solar powered cars in Australia. In 1999 the largest plant was developed producing more than 20 kilowatts.

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In 1999, the most proficient solar cell was developed with a photo-voltaic efficiency of 36 percent, now a day we produce 200 megawatts to 600 megawatts electricity from solar energy like in India’s Gujarat Solar Park, a compilation of solar farms spotted around the Gujarat region, show a mutual installed capacity of 605 megawatts and Golmud Solar Park in China, with an installed capacity of 200 megawatts.

PV solar cells A single solar cell cannot provide required useful output. So to increase output power level of a PV system, it is required to connect number of such PV solar cells. A solar module is normally series connected sufficient number of solar cells to provide required standard output voltage and power.

One solar module can be rated from 3 watts to 300 watts.

The solar modules or PV modules are commercially available basic building block of a solar electric power generation system. Actually a single solar PV cell generates very tiny amount that is around 0.1 watt to 2 watts.

But it is not practical to use such low power unit as building block of a system.

So required number of such cells are combined together to form a practical commercially available solar unit which is known as solar module or PV module.

In a solar module the solar cells are connected in same fashion as the battery cell units in a battery bank system. That means positive terminals of one cell connected to negative terminal voltage of solar module is simple sum of the voltage of individual cells connected in series in the module.

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The normal output voltage of a solar cell is approximately 0.5 V hence if 6 such cells are connected in series then the output voltage of the cell would be 0.5 Ă— 6 = 3 Volt.

V-I Characteristic of Solar Module If we draw a graph by taking X-axis as voltage axis and Y-axis as currents of a solar module, then the graph will represent V-I characteristic of a solar module.

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Short Circuit Current of PV Module Under Standard Test Condition positive and negative terminal of a solar module are short circuited, then the current delivered by the module is short circuit current.

Bigger value of this current indicates a better module.

Although under standard test condition, this current also depends upon the area of the module exposed to the light. As it depends upon area, it is better to express by short circuit current per unit area.

This is deneted as Jsc.

Hence,

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Where, A is the area of the module exposed to the standard light radiation (1000w/m2). Short circuit current of a pv module also depends upon solar cell manufacturing technology.

Open Circuit Voltage (Voc)

The voltage output of a solar module under standard test condition, when the terminals of the modules are not connected with any load. This rating of solar module mainly depends upon the technology used to manufacture solar cells of the module. More Voc indicates betterness of the solar module. This open circuit voltage of a solar module also depends upon operating temperature.

Maximum Power Point This is the maximum amount of power which can deliver by the module Under Standard Test Conditions. For a fixed dimension of a module higher the maximum power better the module.

Maximum power also called peak power and this is denoted as Wm or Wp. A solar module can be operated in any voltage and current combination upto Voc and Isc.

But for a particular current and voltage combination under standard conditions the output power is maximum. If we proceed through y-axis of the V-I characteristic of a solar module, we will find the power output increases nearly linearly with current but after a certain current power output will fall down as it approaches to the short circuit current as at short circuit condition the voltage is considered to be ideally zero across the terminals of the solar module. So it is clear that maximum output power of a solar module does not occur at maximum current i.e. short circuit current instead it

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occurs at certain current which is less than short circuit current (Isc). This current at which maximum output power occurs is denoted as Im. Similarly maximum power of a solar cell does not occur at open circuit voltage as it is open circuit condition and current through the cell is considered to be ideally zero, at this condition. But similarly as previous case, maximum power in a solar module occurs at a voltage lower than open circuit voltage (Voc). The voltage at which maximum power output occurs is denoted as Vm. The maximum power of a solar module is given as The current and voltage at which maximum power occurs are referred as, current and voltage at maximum power point respectively.

Efficiency of Solar Module

Efficiency of solar module is defined as the ratio of maximum power at standard test condition, to the input power. Input power of a solar module is solar radiation which is considered as 1000 w/m2. So, actual input power to the cell is 1000A W. Where, A is the exposed area of the solar

module.Therefore, efficiency, 9

Number of Cells in Module Number of cells in a module depends upon the standard voltage requirement per module. In 1980’s solar modules were mainly manufactured for charging 12 Volt batteries. But for charging a 12 Volt battery it is required to have sufficiently higher output voltage of the module than 12 Volt. It was standard practice to design a solar module with maximum voltage rating (Vm) of 15 Volt. This module of 15 Volt becomes standard module from those days.

The number of solar cells to be connected in series to achieve standard voltage output depends upon the open-circuit voltage (Voc) of the individual cells.

The Voc of a solar cell depends upon mainly its manufacturing techniques. The table below shows the open-circuit voltage of different solar cells at standard test conditions.

Solar Cell Types

Open Circuit Voltage at STC

Mono Crystalline Silicon Solar Cell

0.55 to 0.68 V

Poly Crystalline Silicon Solar Cell

0.55 to 0.65 V

Amorphous Silicon Solar Cell

0.7 to 1.1 V

Cadmium Telluride Solar Cell

0.8 to 1.0 V

Copper Indium Gallium Selenide Solar Cell

0.5 to 0.7 V

Gallium Indium Phosphide/ Gallium Arsenide / Gallium Solar Cell

1 to 2.5 V

For a crystalline solar cell the open-circuit voltage, is about 0.5 V, as shown in the table above. The voltage Voc is mentioned at 25oC but at the temperature higher than 25oC the value of this voltage drops nearly by 0.08 V. So at normal operating temperature the voltage available across the terminals of each crystalline solar cell is Now, it is standard to make a solar module which can give 15 V opencircuit voltage at any condition. Hence, the required number of solar cells to construct such solar module is,

So, 36 numbers of crystalline solar cells are required to build a standard solar module of 15 V.

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TYPES OF SOLAR POWR STATIONS There are mainly four types of solar power stations.

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2.

3.

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Stand Alone or Off Grid type Solar Power Plant Grid Tie type Solar Power Plant Grid Tie with Power Backup or Grid Interactive type Solar Power Plant Grid Fallback type Solar Power Plant.

1. Stand Alone or Off Grid Solar Power Station This is most commonly used photo-voltaic installation used to provide localized electricity in absence of conventional source of electric power at certain location. As the name prefers this system does not keep any direct or indirect connection with any grid type network.

In standalone system the solar modules produce electric energy which is utilized to charge a storage battery and this battery delivers electricity to the connected load. Standalone systems are normally small system with less than 1 kilo watt generation capacity.

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2. Grid Tie Solar Power Station In some countries facility is available of selling power to the local or national grid. This is gaining popularity in Europe and the United States. This system facilitates both electric utility companies as well as the consumers. Here consumers can generate electricity by their own plant and can sell the surplus to the electricity utility company through grid connected to their plant.

As the consumers sell the power they can earn money as return of their investment for installation of captive power plant on the other hand electric utility companies can reduce their capital investment on their own plant for power generation. In a grid-tie solar system, consumers consume electricity produced by solar captive power plant during sunny day time and also export surplus energy to grid but at night while solar plant does not produce energy, they import electric energy from grid for consumption. The main disadvantage of this system is that if there is a power cut in the grid, the solar modules should be disconnected from the grid. This system is not always very profitable especially where overall maximum demand of the system does not occur at the peak sunny period of the day. In hot climate where the power demand for air conditioning machines becomes maximum during peak sunny period of the day, this grid tie solar power generation system works most efficiently.

Grid tie solar systems are of two types one with single macro central inverter and other with multiple micro inverters. In the former type of solar system, the solar panels as well as grid supply are connected to a common central inverter called grid tie inverter as shown below. The inverter here converts the DC of the solar panel to grid level AC and then feeds to the grid as well as the consumer’s distribution panel depending upon the instant demand of the systems. Here grid-tie inverter also monitors the power being supplied from the grid. If it finds any power cut in the grid, it actuates switching system of the solar system to disconnect it from the grid to ensure no solar electricity can be fed back to the grid during power cut. There is on energy meter connected in the main grid supply line to record the energy export to the grid and energy import from the grid.

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As we already told there is another type of grid-tie system where multiple micro-inverters are used.

Here one micro inverter is connected for each individual solar module. The basic block diagram of this system is very similar to previous one except the micro inverters are connected together to produce desired high AC voltage. In previous case the low direct voltage of solar panels is first converted to alternating voltage then it is transformed to high alternating voltage by transformation action in the inverter itself but in this case the individual alternating output voltage of micro inverters are added together to produce high alternating voltage.

3. Grid Tie with Power Backup Solar Power Generation It is also called grid interactive system. This is a combination of a grid-tie solar power generation unit and storage battery bank. As we said, the main drawback of grid tie system is that when there is any power cut in the grid the solar module is disconnected from the system. For avoiding discontinuity of supply during power cut period one battery bank of sufficient capacity can be connected with the system as power backup.

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4. Grid Fallback Solar Power Generation Grid fallback is most reliable and stable system mainly used for electrifying smaller households.

Here solar modules charge a battery bank which in turn supplies distribution boards through an inverter. When the batteries are discharged to a pre-specified level, the system automatically switches back to the grid power supply. The solar modules then recharge the batteries and after the batteries are being charged up to a pre-specified level again the system switches back to solar power.

We do not sell electricity back to the electricity utility companies through this system. All the power that we produce is utilized for ourselves only.

Although we do not have any direct earning benefit from this system but the system has its own big advantages. This system is most popular where there is no facility of selling power to the grid.

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Grid fallback system has all advantages of grid interactive system except power selling, but it adds benefit of using own power whenever it is required irrespective of position and condition of sun in the sky.

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SOLAR POWER THERMAL PLANTS Technology Fundamentals Most techniques for generating electricity from heat need high temperatures to achieve reasonable efficiencies. The output temperatures of non-concentrating solar collectors are limited to temperatures below 200°C. Therefore, concentrating systems must be used to produce higher temperatures. Due to their high costs, lenses and burning glasses are not usually used for large-scale power plants, and more cost-effective alternatives are used, including reflecting concentrators.

The reflector, which concentrates the sunlight to a focal line or focal point, has a parabolic shape; such a reflector must always be tracked. In general terms, a distinction can be made between one-axis and two-axis tracking: one-axis tracking systems concentrate the sunlight onto an absorber tube in the focal line, while two-axis tracking systems do so onto a relatively small absorber surface near the focal point (see Figure 1).

FIGURE 1. Concentration of sunlight using (a) parabolic trough collector (b) linear Fresnel collector (c) central receiver system with dish collector and (d) central receiver system with distributed reflectors 16

The theoretical maximum concentration factor is 46,211. It is finite because the sun is not really a point radiation source. The maximum theoretical concentration temperature that can be achieved is the sun’s surface temperature of 5500°C; if the concentration ratio is lower, the maximum achievable temperature decreases. However, real systems do not reach these theoretical maxima. This is because, on the one hand, it is not possible to build an absolutely exact system, and on the other, the technical systems which transport heat to the user also reduce the receiver temperatures. If the heat transfer process stops, though, the receiver can reach critically high temperatures.

Parabolic Trough Power Plants Parabolic trough power plants are the only type of solar thermal power plant technology with existing commercial operating systems until 2008. In capacity terms, 354 MWe of electrical power are installed in California, and a plenty of new plants are currently in the planning process in other locations.

The parabolic trough collector consists of large curved mirrors, which concentrate the sunlight by a factor of 80 or more to a focal line. Parallel collectors build up a 300–600 meter long collector row, 17

and a multitude of parallel rows form the solar collector field. The one-axis tracked collectors follow the sun.

The collector field can also be formed from very long rows of parallel Fresnel collectors. In the focal line of these is a metal absorber tube, which is usually embedded in an evacuated glass tube that reduces heat losses. A special high-temperature, resistive selective coating additionally reduces radiation heat losses.

In the Californian systems, thermo oil flows through the absorber tube. This tube heats up the oil to nearly 400°C, and a heat exchanger transfers the heat of the thermal oil to a water steam cycle (also called Rankine cycle). A feedwater pump then puts the water under pressure. Finally, an economizer, vaporizer and superheater together produce superheated steam. This steam expands in a two-stage turbine; between the high-pressure and low-pressure parts of this turbine is a reheater, which heats the steam again. The turbine itself drives an electrical generator that converts the mechanical energy into electrical energy; the condenser behind the turbine condenses the steam back to water, which closes the cycle at the feedwater pump.

It is also possible to produce superheated steam directly using solar collectors.

This makes the thermo oil unnecessary, and also reduces costs because the relatively expensive thermo oil and the heat exchangers are no longer needed. However, direct solar steam generation is still in the prototype stage.

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Guaranteed Capacity In contrast to photovoltaic systems, solar thermal power plants can guarantee capacity (see Figure 2).

During periods of bad weather or during the night, a parallel, fossil fuel burner can produce steam; this parallel burner can also be fired by climate-compatible fuels such as biomass, or hydrogen produced by renewables. With thermal storage, the solar thermal power plant can also generate electricity even if there is no solar energy available.

FIGURE 2. Typical output of a solar thermal power plant with two-hour thermal storage and backup heater to guarantee capacity A proven form of storage system operates with two tanks. The storage medium for high-temperature heat storage is molten salt. The excess heat of the solar collector field heats up the molten salt, which is pumped from the cold to the hot tank.

If the solar collector field cannot produce enough heat to drive the turbine, the molten salt is pumped back from the hot to the cold tank, and heats up the heat transfer fluid. Figure 3 shows the principle of the parabolic trough power plant with thermal storage.

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FIGURE 3. Schematic of a concentrated solar thermal trough power plant with thermal storage

Solar Thermal Tower Power Plants In solar thermal tower power plants, hundreds or even thousands of large two-axis tracked mirrors are installed around a tower. These slightly curved mirrors are also called heliostats; a computer calculates the ideal position for each of these, and a motor drive moves them into the sun. The system must be very precise in order to ensure that sunlight is really focused on the top of the tower. It is here that the absorber is located, and this is heated up to temperatures of 1000°C or more.

Hot air or molten salt then transports the heat from the absorber to a steam generator; superheated water steam is produced there, which drives a turbine and electrical generator, as described above for the parabolic trough power plants.

Only two types of solar tower concepts will be described here in greater detail.

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Dish-Stirling prototype systems in Spain

Solar Chimney Power Plants

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All three technologies described above can only use direct normal irradiance. However, another solar thermal power plant concept – the solar chimney power plant – converts global irradiance into electricity. Since chimneys are often associated negatively with exhaust gases, this concept is also known as the solar power tower plant, although it is totally different from the tower concepts described above. A solar chimney power plant has a high chimney (tower), with a height of up to 1000 metres, and this is surrounded by a large collector roof, up to 130 metres in diameter, that consists of glass or resistive plastic supported on a framework (see artist’s impression). Towards its centre, the roof curves upwards to join the chimney, creating a funnel.

The sun heats up the ground and the air underneath the collector roof, and the heated air follows the upward incline of the roof until it reaches the chimney. There, it flows at high speed through the chimney and drives wind generators at its bottom. The ground under the collector roof behaves as a storage medium, and can even heat up the air for a significant time after sunset. The efficiency of the solar chimney power plant is below 2%, and depends mainly on the height of the tower, and so these power plants can only be constructed on land which is very cheap or free. Such areas are usually situated in desert regions.

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However, the whole power plant is not without other uses, as the outer area under the collector roof can also be utilized as a greenhouse for agricultural purposes. As with trough and tower plants, the minimum economical size of solar chimney power plants is also in the multi-megawatt range.

THE LATEST IN SOLAR TECHNOLOGY Solar technologies have evolved a lot since they first made their debut in the 1960s. While previously solar photovoltaic (PV) were seen as a thing of the future, today, technological breakthroughs have positioned the industry for huge growth.

A series of new developments in solar PV technology also promise to contribute to the industry's success.

Advances in Solar Cell Technology Researchers have longed looked for ways to improve the efficiency and cost-effectiveness of solar cells - the life blood of solar PV systems. A solar PV array is comprised of hundreds, sometimes thousands of solar cells, that individually convert radiant sun light into electrical currents. The average solar cell is approximately 15% efficient, which means nearly 85% of the sunlight that hits them does not get converted into electricity. As such, scientists have constantly been experimenting with new technologies to boost this light capture and conversion.

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Light-Sensitive Nanoparticles. Recently, a group of scientists at the University of Toronto unveiled a new type of light-sensitive nanoparticle called colloidal quantum dots, that many believe will offer a

less expensive and more flexible material for solar cells. Specifically, the new materials use n-type and p-type semiconductors - but ones that can actually function outdoors. This is a unique discovery since previous designs weren't capable of functioning outdoors and therefore not practical applications for the solar market. University of Toronto researchers discovered that n-type materials bind to oxygen - the new colloidal quantum dots don't bind to air and therefore can maintain their stability outside. This helps increase radiant light absorption. Panels using this new technology were found to be up to eight percent more efficient at converting sunlight.

Gallium Arsenide. Researchers at Imperial College University in London believe they have discovered a new material - gallium arsenide - that could make solar PV systems nearly three times more efficient than existing products on the market. The solar cells are called "triple junction cells" and they're much more efficient, because they can be chemically altered in a manner that optimizes sunlight capture. The 24

model uses a sensor-driven window blind that can track sun light along with "light-pipes" that guide the light into the system.

Advances in Energy Storage Another major focus of scientists is to find new ways to store energy produced by solar PV systems.

Currently, electricity is largely a "use it or lose it" type resource whereby once it's generated by a solar PV system (or any type of fuel source) the electricity goes onto the grid and must be used immediately or be lost. Since the sunlight does not shine twenty four hours a day, this means that most solar PV systems are only meeting electrical demands for a portion of the day - as a result, a lot of electricity is lost, if it's not used. There are a number of batteries on the market that can store this energy, but even the most high-tech ones are fairly inefficient; they're also expensive and have a pretty short shelf life, making them not the most attractive options for utility companies and consumers. That is why scientists are exploring different ways to store this electricity so that it can be used on demand.

Molten Salt Storage Technology. A company called Novatec Solar recently commissioned a promising energy storage solution for solar PV systems using a molten salt storage technology. The process uses inorganic salts to transfer energy generated by solar PV systems into solar thermal using heat transfer fluid rather than oils as some storage system have. The result is that solar plants can operate at temperatures over 500 degrees Celsius, which would result in a much higher power output. This means that costs to store solar would be lowered significantly and utility companies could finally use solar power plants as base load plants rather than to meet peak demand during prime daylight hours.

Solar Panel with Built-In Battery. In a project funded by the United States Department of Energy, Ohio State University researchers recently announced they created a battery that is 20% more efficient and 25% cheaper than anything on the market today. The secret to the design is that the rechargeable battery is built into the solar panel itself, rather than operating as two standalone systems. By conjoining the two into one system, scientists said they could lower costs by 25% compared to existing PRODUCTS.

Advances in Solar Cell Manufacturing Another area that has made solar PV technologies cost prohibitive compared to traditional fuel sources is the manufacturing process. Scientists are also focused on ways

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to improve the efficiency of how solar components are manufactured.

Magnesium Chloride. While over ninety percent of solar panels on the market today are comprised of silicon semiconductors, the key ingredient to converting sunlight into electricity, many believe the next generation of solar panels will be made of a thin film technology that uses narrow coatings of cadmium telluride in solar cells - this technology promises to be a much cheaper and more efficient way to engage the photovoltaic process. One major obstacle for cadmium telluride thin film cells is that they become highly unstable during the manufacturing process, which currently uses cadmium chloride.

Researchers have devised a new, safe and seemingly low cost way to overcome this hurdle by using a material called magnesium chloride in replace of cadmium chloride. Magnesium chloride is recovered from seawater, an abundant resource, which makes the resource very low cost, as well as non-toxic. Replacing the manufacturing process with this material promises to increase the efficiency of these solar cells from two percent to up to fifteen percent.

New Solar Applications When most people think of solar PV systems they think of them atop roofs or mounted for industrial scale use. But researchers are exploring a number of unconventional solar applications that could promise to transform the industry.

Solar Roadways. Scientists are exploring ways to actually line highways and roads with solar panels that would then be used to deploy large amounts of electricity to the grid. This would help overcome a major barrier to industrial scale solar, which opponents say threatens to take up too much land. Solar roadways have already popped up in the Netherlands.

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Floating Solar. Another way to address land use concerns associated with wide scale solar is to erect solar plants on the water, since over 70% of the Earth's surface is covered in water. Some researchers, including a French firm called Ciel et Terre, are experimenting with this technology.

The company has projects set up in France, Japan, and England and other parts of the world are also piloting projects including a project in India and California in the U.S. Space Based Solar. Scientists are resurrecting a technology that was first tested over forty years ago in which space-based satellites capture sunlight and convert it into microwave energy that is then beamed back to earth.

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This type of technology promises to capture significant more amount of sunlight (nearly ninety percent) since satellites can be positioned to optimize light capture round the clock. India, China and Japan are investing heavily in these technologies right now.

10 TECHNOLOGIES SHAPING THE FUTURE OF SOLAR POWER 1. Bio-solar cells For the first time ever, researchers connected nine biological-solar (bio-solar) cells into a bio-solar panel and continuously produced electricity from the panel and generated the most wattage of any existing small-scale bio-solar cells.

Last year, the group took steps towards building a better bio-solar cell by changing the materials used in anodes and cathodes (positive and negative terminals) of the cell and also created a miniature microfluidic-based single-chambered device to house the bacteria instead of the conventional, dualchambered bio-solar cells.

However, this time, the group connected nine identical bio-solar cells in a 3x3 pattern to make a scalable and stackable bio-solar panel. The panel continuously generated electricity from photosynthesis and respiratory activities of the bacteria in 12-hour day-night cycles over 60 total hours.

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The current research is the latest step in using cyanobacteria—which can be found in almost every terrestrial and aquatic habitat on earth—as a source of clean and sustainable energy.

Even with the breakthrough, a typical “traditional” solar panel on the roof of a residential house, made up of 60 cells in a 6x10 configuration, generates roughly 200 watts of electrical power at a given moment. The cells from this study, in a similar configuration, would generate about 0.00003726 watts. So, it isn’t efficient just yet, but the findings open the door to future research of the bacteria itself.

“Once a functional bio-solar panel becomes available, it could become a permanent power source for supplying long-term power for small, wireless telemetry systems as well as wireless sensors used at remote sites where frequent battery replacement is impractical,” said Seokheun ‘Sean’ Choi, an assistant professor of electrical and computer engineering in Binghamton University’s Thomas J. Watson School of Engineering and Applied Science, and co-author of the paper, in a 11 April press statement.

2. A new way for converting solar energy into electricity Researchers from The Hebrew University of Jerusalem in Israel, and the University of Bochum in Germany, reported a new paradigm for the development of photo-bioelectrochemical cells in Nature Energy this January, providing a means for the conversion of solar energy into electricity.

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While photosynthesis is the process by which plants and other organisms make their own food using carbon dioxide, water and sunlight, bioelectrochemical systems take advantage of biological capacities (microbes, enzymes, plants) for the catalysis of electrochemical reactions.

In a 19 January press statement, the researchers pointed out that although significant progress has been achieved in the integration of native photosystems with electrodes for light-to-electrical energy conversion, uniting photosystems with enzymes to yield photo-bioelectrocatalytic solar cells remains a challenge.

Hence, the researchers constructed photo-bioelectrochemical cells using the native photosynthetic reaction and the enzymes glucose oxidase, or glucose dehydrogenase. The system comprises modified integrated electrodes that include the natural photosynthetic reaction centre, known as photosystem I, along with the enzymes. The native proteins are electrically wired by means of chemical electron transfer mediators. Photo-irradiation of the electrodes leads to the generation of electrical power, while oxidizing the glucose substrate acts as a fuel.

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3. Reshaping solar spectrum to turn light into electricity Land and labour costs account for the bulk of the expense when installing solar panels since solar cells—made often of silicon or cadmium telluride—rarely account for more than 20% of the total cost. Hence, solar energy could be made cheaper if less land had to be purchased to accommodate the panels. This is best achieved if each solar cell generates more power, but it is not easy.

A team of chemists at the University of California says it has found a way to make this happen. In a paper that was published in Nano Letters, an American Chemical Society publication, the researchers said that by combining inorganic semiconductor nanocrystals with organic molecules, they succeeded in “upconverting” (two low-energy photons into one high-energy photon) photons in the visible and near-infrared regions of the solar spectrum.

The infrared region of the solar spectrum passes right through the photovoltaic materials that make up today’s solar cells, explained Christopher Bardeen, a professor of chemistry in a press release on 27 July 2015. This upconverted photon is readily absorbed by photovoltaic cells, generating electricity from light that normally would be wasted, according to Bardeen.

He added that these materials are essentially “reshaping the solar spectrum” so that it better matches the photovoltaic materials used today in solar cells. The ability to utilize the infrared portion of the solar spectrum could boost solar photovoltaic efficiencies by 30% or more.

Besides solar energy, the ability to upconvert two low-energy photons into one high-energy photon has potential applications in biological imaging, data storage and organic light-emitting diodes, says Bardeen.

4. WaterNest 100 Indian real estate developers can take a lesson or two from this project. EcoFloLife has developed the WaterNest 100 eco-friendly floating house, exclusively designed by renowned Italian architect Giancarlo Zema. It is an over 100 sq. m residential unit, 12 metres in diameter and 4 metres high, made entirely of recycled laminated timber and a recycled aluminium hull.

Balconies are conveniently located on the sides and thanks to the large windows, permit enjoyment of fascinating views over the water. Bathroom and kitchen skylights are located on the wooden roof, as well as 60 sq. m of amorphous photovoltaic panels capable of generating 4kWp, which are used for the internal needs of the floating house. The interior of WaterNest 100 floating house can include a living room, dining area, bedroom, kitchen and bathroom or have other configurations according to the different housing or working needs.

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The floating house can be positioned along river courses, lakes, bays, atolls and sea areas with calm waters. The use of materials and sustainable production systems make this unit recyclable up to as much as 98%. It has a hull that is made entirely of aluminium—a light alloy, highly resistant to impact, corrosion and 100% recyclable. Its photovoltaic panels installed on the wooden roof differ from conventional ones due to the low-energy consumption required for their production. From an aesthetic point of view, they can be curved to fit almost any type of roofing.

5. Floating panels, floating solar farms In many countries, there is a lack of space to install large-scale ground-mount solar systems. As authorities wish to avoid taking away large farmlands for ground-mount solar systems, companies are introducing ecological alternative solutions.

One such firm is French company Ciel & Terre International, which has been developing large-scale floating solar solutions since 2011. Its Hydrelio Floating PV system allows standard PV panels to be 32

installed on large bodies of water such as drinking water reservoirs, quarry lakes, irrigation canals, remediation and tailing ponds, and hydroelectric dam reservoirs.

This simple and affordable alternative to ground-mounted systems is particularly suitable for waterintensive industries that cannot afford to waste either land or water.

This is how it works. The main float is constructed of high-density thermoplastic (HDPE) and is set at a 12-degree angle to support a standard 60-cell PV solar module. A secondary non-slip HDPE float is then used to link the main floats together and provide a platform for maintenance and added buoyancy.

According to Ciel and Terre, the system is easy to install and dismantle, can be adapted to any electrical configuration, is scalable from low- to high-power generation and requires no tools or heavy equipment. It is also eco-friendly, fully recyclable, has low environmental impact and is costeffective.

To date, the system has been installed in the UK. The company has also set up projects for floating solar farms in countries such as India, France and Japan.

6. Transmitting solar power wirelessly from space The Japanese Space Agency (JAXA)’s Space Solar Power Systems (SSPS) aims at transmitting energy from orbiting solar panels by 2030. On 12 March, Mitsubishi Heavy Industries Ltd (MHI) successfully conducted a ground demonstration test of “wireless power transmission”, a technology that will serve as the basis for the SSPS. In the test, 10kW of electricity was successfully transmitted via a microwave unit.

Power reception was confirmed at a receiver located 500 metres away. LED lights on the receiver confirmed the transmission. This marks a new milestone in transmission distance and power load (enough to power a set of conventional kitchen appliances).

Potentially, a solar battery in orbit (36,000km above earth) could generate power that would then be transmitted to earth via microwave/laser, without relying on cables. JAXA anticipates that this new technology could become a mainstay energy source that will simultaneously solve both environmental and energy issues on earth.

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The estimated lifecycle carbon dioxide emission for the operational SSPS indicates that it is almost the same as from nuclear power system and much less than fossil fuel power system, JAXA claims on its website. Countries such as India, China and Japan are investing heavily in these technologies right now.

7. Solar energy harvesting trees Researchers at the VTT Technical Research Centre in Finland have used solar and 3D printing technologies to develop prototypes of what they have christened as “energy harvesting trees�. The tiny leaves generate and store solar energy and can be used to power small appliances and mobile devices. They flourish indoors and outdoors and can also harvest kinetic energy from wind and temperature changes in the surrounding environment.

The tree’s leaves are actually flexible organic solar cells, printed using well-established massproduction techniques. Each leaf has a separate power converter, creating a multi-converter system that makes it possible to collect energy from a variety of sources such as solar, wind and heat temperature.

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The more solar panels there are in a tree, the more energy it can harvest. The tree trunk is made with 3D technology by exploiting wood-based biomaterials VTT has developed. They are mass producible and can be infinitely replicated.

8. Squeezing more out of the sun The sun is undoubtedly the greatest sustainable energy source for earth, but the problem is the low efficiency: 80% of installed PV panels worldwide have a performance of 15% or lower; if the panels are not tracked with the sun, the average of annual tilt losses add up to minus 70%.

German architect Andre Broessel believes he has a solution.

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He says his company Rawlemon can “squeeze more juice out of the sun”, even during the night hours and in low-light regions. He has created a spherical sun power generator prototype called the beta.ray. His technology will combine spherical geometry principles with a dual axis tracking system, allowing twice the yield of a conventional solar panel in a much smaller surface area.

The futuristic design is fully rotational and is suitable for inclined surfaces, walls of buildings, and anywhere with access to the sky. It can even be used as an electric car charging station.

By using a high-efficiency multi-junction cell, Broessel’s company claims to have reduced the cell surface down to 1% compared to the same power output as a conventional silicon cell in optimal conditions.

“In combination with dual axis tracking, our system generates twice the yield of a conventional panel. In addition, our smaller cell area has a lower carbon footprint because its production requires fewer precious semiconductor or other building materials,” he says on the company website.

Rawlemon has also introduced a USB spherical sun charger called beta.ey.

9. Ways to boost solar power A group of scientists at the University of Toronto have unveiled a new type of light-sensitive nanoparticles called colloidal quantum dots, which many believe will offer a less expensive and more flexible material for solar cells. Specifically, the new materials use n-type and p-type semiconductors, but ones that can actually function outdoors. This is possible because the new colloidal quantum dots don’t bind to air (unlike traditional n-type materials that bind to oxygen)—a quality that also helps increase radiant light absorption besides offering stability outdoors. The researchers claim that panels using this new technology were found to be up to 8% more efficient at converting sunlight.

Researchers at Imperial College University in London believe they have discovered a new material— gallium arsenide—that could make solar PV systems nearly three times more efficient than existing products on the market.

The solar cells are called “triple junction cells” and they are much more efficient because they can be chemically altered in a manner that optimizes sunlight capture. The model uses a sensor-driven window blind that can track sun light along with “light-pipes” that guide the light into the system.

A company called Novatec Solar recently commissioned an energy storage solution for solar PV systems using a molten salt storage technology. The process uses inorganic salts to transfer energy 36

generated by solar PV systems into solar thermal using heat transfer fluid rather than oils as some storage systems have. The result is that solar plants can operate at temperatures over 500 degree Celsius, which would result in a much higher power output. This means that costs to store solar power would be lowered significantly and utility companies could finally use solar power plants as base load plants rather than to meet peak demand during prime daylight hours.

In a project funded by the US department of energy, Ohio State University researchers recently announced they created a battery that is 20% more efficient and 25% cheaper than anything on the market today. The secret to the design is that the rechargeable battery is built into the solar panel itself, rather than operating as two stand-alone systems. By conjoining the two into one system, scientists said they could lower costs by 25% compared to existing products.

Scientists are exploring ways to actually line up highways and roads with solar panels, which would then be used to deploy large amounts of electricity to the grid. Called solar roadways, they have already popped up in countries such as the Netherlands and promise to save on land space.

10. Concentrated PV cells IBM researchers have found a way to make concentrated PV cells that are more efficient in converting the sun’s energy into electricity. The researchers have shown that it is possible to increase the concentration of light on photovoltaic cells by about 10 times without causing them to melt. This, they say, makes it possible to boost the amount of usable electrical energy produced by up to five times.

The principle behind concentrated PV cells is to use a large lens to focus light onto a relatively small piece of PV semiconductor material. The benefit is that only a fraction of the semiconductor material is used, thereby reducing costs. IBM’s solution is to place an ultrathin layer of liquid metal, a compound of gallium and indium, between the two surfaces.

The metal has a very high thermal conductivity and because it’s a liquid, it is possible to make this layer extremely thin, typically around 10 micrometers.

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IBM is in talks with solar-cell companies about licensing the technology. Last September, Swissbased Airlight Energy said it has partnered with IBM to bring affordable solar technology to the market by 2017.

The system can concentrate the sun’s radiation 2,000 times and convert 80% of it into useful energy to generate 12kW of electrical power and 20kW of heat on a sunny day—enough to power several average homes.

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WIND ENERGY Windmills at Kinderdijk in the Netherlands Dating from 1740 Used for Pumping Water from the Polder Source - Birds As Art Though modern technology has made dramatic improvements to the efficiency of windmills which are now extensively use for electricity generation, they are still dependent on the vagaries of the weather. Not just on the wind direction but on the intermittent and unpredictable force of the wind. Too little wind and they can't deliver sufficient sustained power to overcome frictional losses in the system. Too much and they are susceptible to damage.

Between these extremes, cost efficient installations have been developed to extract energy from the wind.

Available Power From the Wind Theoretical Power The power P available in the wind impinging on a wind driven generator is given by: P = ½CAρv3 where C is an efficiency factor known as the Power Coefficient which depends on the machine design, A is the area of the wind front intercepted by the rotor blades (the swept area), ρ is the density of the air (averaging 1.225 Kg/m3 at sea level) and v is the wind velocity.

Note that the power is proportional to area swept by the blades, the density of the air and to the cube of the wind speed. Thus doubling the blade length will produce four times the power and doubling the wind speed will produce eight times the power.

Note also that the effective swept area of the blades is an annular ring, not a circle, because of the dead space around the hub of the blades.

A similar equation applies to the theoretical power generated by a "run of river" and "tidal flow" hydro turbines.

Energy Conversion Practical Power and Conversion Efficiency 39

In practical designs, inefficiencies in the design and frictional losses will reduce the power available from the wind still further. Converting this wind power into electrical power also incurs losses of up to 10% in the drive train and the generator and another 10% in the inverter and cabling. Furthermore, when the wind speed exceeds the rated wind speed, control systems limit the energy conversion in order to protect the electric generator so that ultimately, the wind turbine will convert only about 30% to 35% of the available wind energy into electrical energy.

Note that the power output from commercially available domestic wind turbines is usually specified at a steady, gust free, wind speed of 12.5 m/s. (Force 6 on the Beaufort scale corresponding to a strong breeze). In many locations, particularly urban installations, the prevailing wind will rarely reach this speed.

Blade Design for Optimum Energy Capture Modern, high capacity wind turbines, such as those used by the electricity utilities in the electricity grid, typically have blades with a cross section similar to the aerofoils used to provide the lift in aircraft wings.

The direction of the apparent wind, that is the incident wind, relative to the chord line of the aerofoil is known as the angle of attack. Just as with aircraft wings, the lift resulting from the incident wind force increases as the angle of attack increases from 0 to a maximum of about 15 degrees at which point the smooth laminar flow of the air over the blade ceases and the air flow over the blade separates from the aerofoil and becomes turbulent. Above this point the lift force deteriorates rapidly while drag increases leading to a stall. See more about the angle of attack.

The tangential velocity S of any blade section at a distance r from the centre of rotation (the root of the blade) is given by S = r Ί where Ί is the angular velocity of rotation in radians.

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For a given wind speed the apparent wind will be different at the root of the blade from the apparent wind at the tip of the blade because the rotational relative wind speed is different.

For a given speed of rotation, the tangential velocity of sections of the blade increases along the length of the blade towards the tip, so that the pitch of the blade must be twisted to maintain the same, optimum angle of attack at all sections along the length of the blade. The blade twist is thus optimised for a given wind speed. As the wind speed changes however, the twist will no longer be optimum. To retain the optimum angle of attack as wind speed increases a fixed pitch blade must increase its rotational speed accordingly, otherwise, for fixed speed rotors, variable pitch blades must be used.

The number of blades in the turbine rotor and its rotational speed must be optimised to extract the maximum energy from the available wind.

While using rotors with multiple blades should capture more wind energy, there is a practical limit to the number of blades which can be used because each blade of a spinning rotor leaves turbulence in its wake and this reduces the amount of energy which the following blade can extract from the wind.

This same turbulence effect also limits the possible rotor speeds because a high speed rotor does not provide enough time for the air flow to settle after the passage of a blade before the next blade comes along.

There is also a lower limit to both the number of blades and the rotor speed. With too few rotor blades, or a slow turning rotor, most of the wind will pass undisturbed through the gap between the blades reducing the potential for capturing the wind energy. The fewer the number of blades, the faster the wind turbine rotor needs to turn to extract maximum power from the wind.

The notion of the Tip Speed Ratio (TSR) is a concept used by wind turbine designers to optimise a blade set to the shaft speed required by a particular electricity generator while extracting the maximum energy from the wind.

The tip speed ratio is given by: Capacity Factor Electrical generating equipment is usually specified at its rated capacity. This is normally the maximum power or energy output which can be generated in optimal conditions. Since a wind turbine rarely works at its optimal capacity the actual energy output over a year will be much less than its rated capacity. Furthermore there will often be periods when the wind turbine can not deliver 41

any power at all. These occur when there is insufficient wind to power the turbine system, or other periods, fortunately only a few, when the wind turbine must be shut down because the wind speed is dangerously high and exceeds the system cut-out speed.

The capacity factor is simply the wind turbine generator's actual energy output for a given period divided by the theoretical energy output if the machine had operated at its rated power output for the same period. Typical capacity factors for wind turbines range from 0.25 to 0.30. Thus a wind turbine rated at 1 MegaWatt will deliver on average only about 250 kiloWatts of power. (For comparison, the capacity factor of thermal power generation is between 0.70 and 0.90) Wind Supply Characteristics Wind speed Though the force and power of the wind are difficult to quantify, various scales and descriptions have been used to characterise its intensity. The Beaufort scale is one measure in common use. The lowest point or zero on the Beaufort scale corresponds to the calmest conditions when the wind speed is zero and smoke rises vertically. The highest point is defined as force 12 when the wind speed is greater than 34 metres per second (122 km/h, 76 mph). as occurs in tropical cyclones when the countryside is devastated by hurricane conditions.

Small wind turbines generally operate between force 3 and force 7 on the Beaufort scale with the rated capacity commonly being defined at force 6 with a wind speed of 12 m/s.

Below force 3 the wind turbine will not generate significant power.

At force 3, wind speeds range from 3.6 to 5.8 m/s (8 to 13 mph). Wind conditions are described as "light" and leaves are in movement and flags begin to extend.

At force 7, wind speeds range from 14 to 17 m/s (32 to 39 mph). Wind conditions are described as "strong" and whole trees are in motion.

With winds above force 7 small, domestic wind turbines should be shut down to prevent damage.

Large turbines used in the electricity grid are designed to work with wind speeds of up to 25 m/s (90 km/h, 56 mph) which corresponds to between force 9 (severe gale, 23 m/s) and force 10 (storm, 27 m/s) on the Beaufort Scale.

Experience shows that for a given height above ground, the frequency at which the wind blows with any particular speed follows a Rayleigh Distribution. An example is shown below.

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Wind Energy Distribution The histogram below shows the resulting distribution of the wind energy content superimposed on the the Rayleigh wind speed distribution (above) which caused it. Unfortunately not all of this wind energy can be captured by conventional wind turbines.

For a given wind speed the wind energy also depends on the elevation of the wind turbine above sea level. This is because the density of the air decreases with altitude and the wind energy is proportional to the air density. This effect is shown in the following histogram.

Location Considerations Generally marine locations and exposed hilltops provide the most favourable wind conditions with wind speeds consistently greater than 5 m/s.

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Turbulent conditions will reduce the amount of energy which can be extracted from the wind reducing in turn the overall efficiency of the system. This is more likely to be the case over land than over the sea. Raising the height of the turbine above the ground effectively lifts it above the worst of the turbulence and improves efficiency.

Domestic wind turbines located between buildings in urban environments rarely operate at peak efficiency suffering from turbulence as well as being shielded from the wind by buildings and trees.

Practical Systems Community/Grid Installations

Vesta 7 MW Wind Turbines with a Rotor Diameters of 164 m (Source The IET) Grid connected systems are dimensioned for average wind speeds 5.5 m/s on land and 6.5 m/s offshore where wind turbulence is less and wind speeds are higher.

While offshore plants benefit from higher sustainable wind speeds, their construction and maintenance costs are higher.

Large scale wind turbine generators with outputs of up to 8 MWe or more with rotor diameters up to164 metres are now functioning in many regions of the world with even larger designs in the pipeline.

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Source US DOE (EERE) Large rotor blades are necessary to intercept the maximum air stream but these give rise to very high tip speeds. The tip speeds however must be limited, mainly because of unacceptable noise levels, resulting in very low rotation speeds which may be as low as 10 to 20 rpm for large wind turbines.

The operating speed of the generator is however is much higher, typically 1200 rpm, determined by the number of its magnetic pole pairs and the frequency of the grid electrical supply. Consequently a gearbox must be used to increase the shaft speed to drive the generator at the fixed synchronous speed corresponding to the grid frequency.

Note that a "synchronous generator" is one whose electrical output frequency is synchronised to its shaft speed. It is not necessarily synchronised to the grid frequency, although that is usually an objective and extra, external controls are necessary to achieve this.

Fixed Speed Wind Turbine Generators

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Variable Speed Wind Turbine Generators A variable speed generator is better able to cope with stormy wind conditions because its rotor can speed up or slow down to absorb the forces when bursts of wind suddenly increase the torque on the system. The electronic control systems will keep the generator's output frequency constant during these fluctuating wind conditions.

Synchronous Generator with In-Line Frequency Control Rather than controlling the turbine rotation speed to obtain a fixed frequency synchronised with the grid from a synchronous generator, the rotor and turbine can be run at a variable speed corresponding to the prevailing wind conditions. This will produce a varying frequency output from the generator synchronised with the drive shaft rotation speed. This output can then be rectified in the generator side of an AC-DC-AC converter and the converted back to AC in an inverter in grid side of the converter which is synchronised with the grid frequency. See following diagram.

The range of wind speeds over which the system can be operated can be extended and mechanical safety controls can be incorporated by means of an optional speed control system based on pitch control of the rotor vanes as used in the fixed speed system described above.

One major drawback of this system is that the components and the electronic control circuits in the frequency converter must be dimensioned to carry the full generator power. The doubly fed induction generator DFIG overcomes this difficulty.

Doubly Fed Induction Generator - DFIG DFIG technology is currently the preferred wind power generating technology. The basic grid connected asynchronous induction generator gets its excitation current from the grid through the stator windings and has limited control over its output voltage and frequency. The doubly fed induction generator permits a second excitation current input, through slip rings to a wound rotor permitting greater control over the generator output.

The DFIG system consists of a 3 phase wound rotor generator with its stator windings fed from the grid and its rotor windings fed via a back to back converter system in a bidirectional feedback loop taking power either from the grid to the generator or from the generator to the grid. See the following diagram.

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Generator Operating Principle The feedback control system monitors the stator output voltage and frequency and provides error signals if these are different from the grid standards. The frequency error is equal to the generator slip frequency and is equivalent to the difference between the synchronous speed and the actual shaft speed of the machine.

The excitation from the stator windings causes the generator to act in much the same way as a basic squirrel cage or wound rotor generator, (See more about the properties of induction generators and how they work.). Without the additional rotor excitation, the frequency of a slow running generator will be less than the grid frequency which provides its excitation and its slip would be positive.

Conversely if it was running too fast the frequency would be too high and its slip would be negative.

The rotor absorbs power from the grid to speed up and delivers power to the grid in order to slow down. When the machine is running synchronously the frequency of the combined stator and rotor excitation matches the grid frequency, there is no slip and the machine will be synchronised with the grid.

Wind Farms Grouping 10 to 100 wind turbines together in so called "wind farms" can lead to savings of 10% to 20% in construction, distribution and maintenance costs.

According to NREL the"footprint" of land needed to provide space for turbine towers, roads, and support structures is typically between 0.1 and 0.2 hectares (0.25 and 0.50 acres) per turbine. With the typical capacity of wind turbines installed in existing wind farms being around 2 MW, it would take a wind farm with 2000 wind turbines covering 200 to 400 hectares (500 to 1000 acres) just to replace the 4000 MWe power generated by the UK's Drax coal fired power station.

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Unfortunately for the economics of wind turbines, the utility company needs to keep the equivalent capacity from other sources (conventional generating stations or batteries) just to keep the grid customers supplied when the wind is not blowing.

Domestic Wind Turbine Installations 1.6 kW Wind Turbine with 2.8 Metre Diameter Rotor by Cyclone Green Power Inc. In a typical domestic system the wind turbine is coupled directly to a three phase asynchronous permanent magnet AC generator mounted on the same shaft.

To save on capital costs, domestic installations do not have variable pitch rotor blades so the rotor speed varies with the wind speed.

The generator output voltage and frequency are proportional to the rotor speed and the current is proportional to the torque on the shaft.

The output is rectified and fed through a buck-boost regulator to an inverter which generates the required fixed amplitude and frequency AC voltage.

Note: There is possible confusion in the classification of the generator. It is actually a synchronous generator because the frequency of its output is directly synchronised with the rotor speed. In this application however it is called an asynchronous generator because the output frequency of the generator is not synchronised with the mains/utility frequency.

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Urban Installations Wind turbine blade sizes in urban applications are usually limited for practical reasons to less than about 1 metre (2 metres diameter) as well as by local planning ordinances and for similar reasons the height of the turbine above ground is limited to just above rooftop level but below treetop level.

Economics A typical domestic installation with a 1.75m swept diameter, (swept area of 2.4m2), costs around £1500 ($2250). At the rated wind speed of 12.5m/s (28 mph) the wind power intercepted will be 2870 Watts, but after taking into account all the unavoidable system losses, the actual electrical output power will be around 1000 Watts. However this is at the upper end of the performance possibilities. Wind turbulence and shielding due to buildings and trees inhibits sustained strong, gust free wind flow and in any case, for most of the time, the wind speed will more likely be towards the lower end of the performance specification at 4 m/s (9 mph), that is a light breeze. At this speed the power output of the system will be about 32 Watts - Not enough to power a single light bulb. For much of the time the power generated could be less than the quiescent power drain of the inverter.

Running with a constant power output of 32 Watts for a full year would generate only 280 kWh (280 Units) of electrical energy worth £28 at today's price of £0.10 ($0.15) per kWh. To put it into perspective, a typical UK household consumes about 5,000 kWh of electrical energy per year.

Carbon Footprints As with solar power, if the investment fails the conventional economic tests, the notion of carbon footprints is often used to justify the expense, based on the potential for reducing the amount of greenhouse gases emitted by alternative methods of power generation.

Rural Installations The economics of rural and remote locations make wind power more attractive than for urban locations. Because of the remoteness, connection to the electricity grid may be impossible or prohibitively expensive. Furthermore, larger, more efficient wind power installations are possible and the prevailing winds will also be higher. See also Stand Alone Systems Hybrid Installations Hybrid systems combining wind and solar power provide energy diversity reducing the risk of power outages. Wind speeds are often high in the winter when the available solar energy is low and low in the summer when the available solar energy is high.

Hybrid systems are discussed in more detail in the section on Remote Area Power Systems

Wind power provides a valuable complement to large scale base load power stations. Where there is an economic back-up, such as hydro power or large scale storage batteries, which can be called upon at very short notice, a significant proportion of electricity can be provided from wind.

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Solar Wind Power: Generating Power In The Future

As the world discovers new ways to meet its growing energy needs, energy generated from Sun, which is better known as solar power and energy generated from wind called the wind power are being considered as a means of generating power. Though these two sources of energy have attracted the scientists for a very long time, they are not able to decide, which of the two is a better source to generate power. Now scientists are looking at a third option as well.

Scientists at Washington State University have now combined solar power and wind power to produce enormous energy called the solar wind power, which will satisfy all energy requirements of human kind.

Advantages of Solar wind power. 

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The scientists say that whereas the entire energy generated from solar wind will not be able to reach the planet for consumption as a lot of energy generated by the satellite has to be pumped back to copper wire to create the electron-harvesting magnetic field, yet the amount that reaches earth is more than sufficient to fulfill the needs of entire human, irrespective of the environment condition.

Moreover, the team of scientists at Washington State University hopes that it can generate 1 billion billion gigawatts of power by using a massive 8,400-kilometer-wide solar sail to harvest the power in solar wind.

According to the team at Washington State University, 1000 homes can be lit by generating enough power for them with the help of 300 meters (984 feet) of copper wire, which is attached to a twometer-wide (6.6-foot-wide) receiver and a 10-meter (32.8-foot) sail.

One billion gigawatts of power could also be generated by a satellite having 1,000-meter (3,280-foot) cable with a sail 8,400 kilometers (5,220 miles) across, which are placed at roughly the same orbit.

The scientists feel that if some of the practical issued are solved, Solar wind power will generate the amount of power that no one including the scientists working to find new means of generating power ever expected.

How does the Solar wind power technology work?

The satellite launched to tap solar wind power, instead of working like a wind mill, where a blade attached to the turbine is physically rotated to generate electricity, would use charged copper wire for capturing electrons zooming away from the sun at several hundred kilometers per second.

Disadvantages of Solar wind power But despite the fact that Solar wind power will solve almost all the problems that we were to face in future due to power generating resources getting exhausted, it has some disadvantages as well. These may include:

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Brooks Harrop, the co-author of the journal paper says that while scientists are keen to tap solar wind to generate power, they also need to keep provisions for engineering difficulties and these engineering difficulties will have to be solved before satellites to tap solar wind power are deployed.

The distance between the satellite and earth will be so huge that as the laser beam travels millions of miles, it makes even the tightest laser beam spread out and lose most of the energy. To solve this problem, a more focused laser is needed.

But even if these laser beams reach our satellites, it is very doubtful that our satellites in their present form will be able to tap them. As Greg Howes, a scientist at the University of Iowa puts it, “The energy is there but to tap that energy from solar wind, we require big satellites. There may be practical constraints in this.

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Bioenergy Introduction Bioenergy is the most widely used renewable source of energy in the world, providing about 10% of the world primary energy supplies. Biomass energy is derived from plant-based material whereby solar energy has been converted into organic matter. Sources include forestry and agricultural crops and residues; byproducts from food, feed, fiber, and materials processing plants; and post-consumer wastes such as municipal solid waste, wastewater, and landfill gas. Biomass can be used in a variety of energy-conversion processes to yield power, heat, steam, and transportation fuels (Figure 1). Traditional biomass already provides the main source of energy for household heating and cooking in many developing nations. It is also used by food processing industries, the animal feed industry, and the wood products industry, which includes construction and fiber products (paper and derivatives), along with chemical products made by these industries that have diverse applications including detergents, fertilizers, and erosion control products.

Step 1. Assess Biomass Resource Availability The development and scale-up of any bioenergy project begins with an analysis of the resource potential. Generally speaking, there are three types of biomass resource potential: theoretical, technical, and economic.

• Theoretical: Illustrates the ultimate resource potential based on calculations of all existing biomass, with no constraints on access or cost-effectiveness.

• Technical: Limits the theoretical resource potential by accounting for terrain limitations, land use and environmental considerations, collection inefficiencies, and a number of other technical and social constraints. This type of potential is also called accessible biomass resource potential.

• Economic: Economic parameters are applied to the technical resource potential, which results in a subset of the technical potential along with an estimate of the cost of biomass resources either at the field or forest edge. The final outcome of this type of assessment is a supply curve ($/tonne).

Products that assess biomass resources have different information characteristics and applicability.

Step 2. Conduct Market Analysis Analyzing the existing and potential markets for biomass resources, along with barriers, is critical when planning a bioenergy program. A thorough understanding of the market size, growth, regional segmentation, and trends relies on many different inputs such as: • State of technology and the country’s experience with each technology • Production cost • Socio-economic and environmental impacts of biomass production and use • Policy framework in support of the biomass industry • Trade opportunities. Evaluate the State of Technology A variety of technologies can transform biomass into energy for residential, commercial, and industrial uses.

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Generally, these technologies fall into four categories, each appropriate for specific biomass types and resulting in specific energy products: • Thermal Conversion: The use of heat to convert biomass material into other forms of energy. This type of conversion includes direct combustion, pyrolysis (heating biomass in the absence of oxygen to produce a liquid bio-oil), and torrefaction (a process of mild pyrolysis resulting in a solid product with a lower moisture content and a higher energy content compared to those in the initial biomass).

• Thermo-chemical Conversion: The use of heat and chemical processes in the production of energy products from biomass. An example of such process is gasification (heating biomass with about one-third of the oxygen necessary for complete combustion, which produces a mixture of carbon monoxide and hydrogen, known as syngas).

• Biochemical Conversion: The use of enzymes, bacteria, and other microorganisms to break down biomass into liquid fuels, chemicals, heat, and electricity. This conversion type includes anaerobic digestion and fermentation.

• Chemical Conversion: The use of chemical agents to transform biomass into other forms of useable energy. An example is the transesterification process, which causes the feedstock (vegetable oils) to react with alcohol (usually methanol) to produce chemical compounds known as fatty acid methyl esters (FAME).

Biodiesel is a common endproduct of transesterification, as are glycerin and soaps. The biomass conversion technologies are in various stages of development. Some of these technologies are in commercial or pre-commercial production, making them cost-competitive, while others are still in the research and development phase. For example, biofuels production from starches and sugars via fermentation and from vegetable oils through transesterification are well-established technologies, while the production of biofuels and drop-in fuels (fuels that can make use of existing refining and distribution) from lignocellulosic material are still in the demonstrational and pilot stages.

Assess Socio-Economic Impacts Particularly because of its potential impact on food production, rural development, and poverty alleviation, a bioenergy project needs to be evaluated based on the benefits it can provide to the society and the economy involved. Bioenergy initiatives affect the communities in which they are implemented in various ways. Potential impacts may include creation or loss of jobs and greater access to energy, as well as impacts on food, feed, and land prices. Bioenergy has the potential to stimulate agricultural productivity, thus it can lead to improving the livelihood of rural populations.

The large-scale use of bioenergy may directly compete with land use, water resources, and labor for food production, which may affect food security if not properly managed. This could have an adverse effect on a country’s economy, particularly in the developing parts of the world, thus it is essential to capture, evaluate, and numerate the social and economic impacts associated with bioenergy production.

Policy Framework in Support of the Biomass Industry National strategic policies and laws that aim to improve the attractiveness and security of bioenergy investments (such as renewable portfolio standards, carbon cap-and-trade policies, blending mandates, and vehicle fuel standards) help achieve the cost-effective and efficient use of biomass resources. Long-term financial incentives and a well-established policy framework for bioenergy are key for attracting investors.

Tax incentives can help overcome the high upfront costs for both producers and distributors. Establishing a low carbon fuel standard can help create a local market for biofuels.

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A strong, long-term institutional framework is also necessary to ensure the coordination and coherence of policies affecting energy, environment, and agricultural practices.

Trade Opportunities The growing bioenergy industry provides many opportunities for local, regional, and international trade. These opportunities come from the diverse nature of the industry–from various feedstocks (including forest products, agricultural products, and biodegradable wastes) to several end products such as power, heat, fuels, and chemicals.

Assessing trade opportunities is an important part of the market analysis: a reliable supply of biomass and a reliable demand for bio-energy is vital to developing stable market activities. In some areas, biomass production potential either cannot meet or exceed the local demand; therefore, a country’s role in the international bioenergy market should be considered when building a bioenergy program.

Step 3. Conduct Feasibility Studies and Roadmap Activities Once a promising bioenergy opportunity is identified, the next step is to conduct a feasibility study or prepare a roadmap. Feasibility studies are comprehensive analyses that provide in-depth details about a project or technology and determine if, and how, it can succeed. A technology roadmap is an illustrative high-level plan that outlines opportunities, barriers, and action items (including necessary R&D activities and policy framework) to achieve desired outcome.

Effective roadmaps are built on existing assets in a country that can be leveraged to drive growth in the region proposed. Feasibility studies are used primarily by industry developers while roadmaps are generally developed by policymakers.

Biomass can be used to produce renewable electricity, thermal energy, or transportation fuels (biofuels). Biomass is defined as living or recently dead organisms and any byproducts of those organisms, plant or animal. The term is generally understood to exclude coal, oil, and other fossilized remnants of organisms, as well as soils. In this strict sense, biomass encompasses all living things. In the context of biomass energy, however, the term refers to those crops, residues, and other biological materials that can be used as a substitute for fossil fuels in the production of energy and other products. Living biomass takes in carbon as it grows and releases this carbon when used for energy, resulting in a carbon-neutral cycle that does not increase the atmospheric concentration of greenhouse gases.

Biomass Energy The energy stored in biomass can be released to produce renewable electricity or heat. Biopower can be generated through combustion or gasification of dry biomass or biogas (methane) captured through controlled anaerobic digestion. Cofiring of biomass and fossil fuels (usually coal) is a low-cost means of reducing greenhouse gas emissions, improving cost-effectiveness, and reducing air pollutants in existing power plants. Thermal energy (heating and cooling) is often produced at the scale of the individual building, through direct combustion of wood pellets, wood chips, and other sources of dry biomass.

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Combined heat and power (CHP) operations often represent the most efficient use of biomass (utilizing around 80 percent of potential energy). These facilities capture the waste heat and/or steam from biopower production and pipe it to nearby buildings to provide heat or to chillers for cooling.

Biofuels A number of transportation fuels can be produced from biomass, helping to alleviate demand for petroleum products and improve the greenhouse gas emissions profile of the transportation sector. Ethanol from corn and sugarcane, and biodiesel from soy, rapeseed, and oil palm dominate the current market for biofuels, but a number of companies are moving forward aggressively to develop and market a number of advanced second-generation biofuels made from non-food feedstocks, such as municipal waste, algae, perennial grasses, and wood chips. These fuels include cellulosic ethanol, bio-butanol, methanol and a number of synthetic gasoline/diesel equivalents. Until we are able to produce a significant amount of electric vehicles that run on renewably-produced electricity, biofuels remain the only widely available source of clean, renewable transportation energy.

Biobased Products Just as biomass can substitute for fossil fuels in the production of energy, it can also provide a renewable substitute for the many industrial products and materials made from petroleum or natural gas – biobased foams, plastics, fertilizers, lubricants, and industrial chemicals are a few of the possibilities.

Biomass Feedstocks Every region has its own locally generated biomass feedstocks from agriculture, forest, and urban sources.

A wide variety of biomass feedstocks are available and biomass can be produced anywhere that plants or animals can live. Furthermore, most feedstocks can be made into liquid fuels, heat, electric power, and/or biobased products. This makes biomass a flexible and widespread resource that can be adapted locally to meet local needs and objectives.

Some of the most common (and/or most promising) biomass feedstocks are:  Grains and starch crops – sugar cane, corn, wheat, sugar beets, industrial sweet potatoes, etc.  Agricultural residues – Corn stover, wheat straw, rice straw, orchard prunings, etc.  Food waste – waste produce, food processing waste, etc.  Forestry materials – Logging residues, forest thinnings, etc.  Animal byproducts – Tallow, fish oil, manure, etc.  Energy crops – Switchgrass, miscanthus, hybrid poplar, willow, algae, etc.

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

Urban and suburban wastes – municipal solid wastes (MSW), lawn wastes, wastewater treatment sludge, urban wood wastes, disaster debris, trap grease, yellow grease, waste cooking oil, etc.

Biomass and Land Use Like wind, solar, and other renewable energy sources, biomass can make a positive impact on our atmosphere by lessening our dependence on climate change-inducing fossil fuels. Biomass energy differs from other renewables, however, in the extent to which its use is directly tied to the farms, forests, and other ecosystems from which biomass feedstocks are obtained. Because of this close association, the use of biomass has the potential to result in a wide range of environmental and social impacts, both positive and negative, above and beyond its use as a substitute for fossil fuels. Impacts on soils, water resources, biodiversity, ecosystem function, and local communities will differ depending on what choices are made regarding what types of biomass are used, as well as where and how they are produced. This is why biomass needs to be produced and harvested as sustainably as possible. In this sense, sustainability refers to choosing management practices that minimize adverse impacts and complement local land-management objectives, such as farm preservation, forest stewardship, food production, and wildlife management.

Another issue heavily associated with biomass production is greenhouse gas emissions from land management and land use change. These refer to emissions of greenhouse gases (especially CO2, CH4, and N2O) resulting from agricultural inputs, management practices, and land use changes associated with production of biomass. These emissions can be divided into direct and indirect sources.

Direct emissions refer to those resulting from land clearing, agricultural inputs (such as fertilizers), or management practices undertaken in the process of growing or harvesting a biomass crop. Indirect emissions are associated with market-driven land use change. These are the emissions that occur when forests, grasslands, or other ecosystems are cleared to produce crops or other commodities to compensate for land that has been diverted to energy production. The effects are difficult to quantify or attribute, making indirect emissions from land use change (ILUC) a very controversial subject.

Finally, it is important to remember that biomass markets will add value to biomass products, residues, and productive lands. This value will help improve the economic viability of working lands and act as a positive incentive to help preserve farms and forests from the accelerating threat of urban and suburban sprawl – the greatest land use impact.

Marine Microalgae: the Future of Sustainable Biofuel Did you know that for 50 percent of the breaths you take, you have the oceans to thank? Scientists believe that marine phytoplankton are responsible for more than half of the oxygen in Earth’s atmosphere!

Photosynthesis from marine organisms is what originally made all life on Earth possible—and now, it may be the thing that helps keep global warming at bay. This is because phytoplankton, also known as marine microalgae, have the potential to provide us with two other things that we desperately need: a mechanism for carbon sequestration, and a source of sustainable energy.

The potential for carbon sequestration comes from the fact that marine microalgae are photosynthetic, meaning that they require light, water, and carbon dioxide to create the nutrients necessary 56

for growth. Culturing large swaths of this algae would create a carbon sink, a reservoir that absorbs more carbon than it releases. This can be likened to planting a new grove of trees. But, unlike trees, microalgae is a highly productive species—they can double their mass on a daily basis, resulting in a growth rate up to 100 times faster than terrestrial plants.

Source: Modified for educational purposes by C.H. Greene from original figure produced by Cellana, LLC.

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Marine microalgae could also be grown on otherwise non-productive, arid land, by using specialized growth chambers such as those illustrated above. This avoids the issue of land competition, since no food crops could be grown in these places. What’s more, marine microalgae do not require freshwater—an expensive and increasingly scarce resource. Instead they thrive on salt water, of which there is plenty (the ocean covers 71 percent of the Earth’s surface). Ribbons of algal cultivation facilities could be built along the shores of desert regions, which have otherwise unproductive land but plenty of sunlight and access to seawater.

There have been some apprehensions, however, which have slowed the progress of algal biofuels. One is that total liquid fuel demand in the United States is incredibly high; many believe algal biofuel will never be able to meet the demand. In 2016, the demand for liquid fuels was approximately 19.6 million barrels per day. Data collected from the Kona demonstration center shows that the productivity of algae is about 0.5 barrels/hectare per day. From these numbers, it is possible to calculate the approximate land area needed to grow enough algae to meet the United States’ liquid fuel demand: 151,352 square miles of land, or about 4 percent of the total U.S. land area (equivalent to about half the size of Texas). To put this in perspective, about 17 percent of U.S. land is currently being used to grow crops. Devoting 4 percent of U.S. land to growing algae might be a stretch, but it is not beyond the realm of possibility, especially if algal facilities are located in otherwise unproductive lands and designed to co-generate other useful products. Moreover, vehicle electrification and better fuel efficiency can help substantially reduce the need for liquid fuels, reducing the impact of biofuels production on the land.

Energy and environmental issues The widespread use of fossil fuels, has brought numerous benefits to industrialized societies. Large amounts of agricultural, domestic and industrial wastes generated in these countries as a result of development, have potentially detrimental effects both on the environment and on human health. Itai-itai and Minamata diseases in Japan, are just two examples of the effects of air and water pollution on human health. The importance of protecting the environment and restoring environmental damage cannot be overemphasized.

In recent years, environmental pollution has become a global problem. Internationalization of industrial and social activities has given rise to problems such as global warming, desertification, and acid deposition. These global problems are rooted in the materially-rich lifestyles which are supported by abundant and wasteful use of fossil fuels in industrialized countries. Rapidly increasing industrial activities in China, India, and in other developing countries implicates that these countries will inevitably contribute to deterioration of the global environment and to destruction of the global ecosystem. Lifestyle changes, and changes in our key industrial systems are required in order to minimize the impact of environmental pollution. The recycling of materials, and thus minimizing the generation of waste, is a basic concept which must be implemented in order to meet the new demands of sustainable development in both industrialized and developing countries.

Mechanisms for implementing this concept and for establishing environmentally compatible technologies which support the future "recycling" world are required. Systems, which utilize energies produced from biomass are typical examples of energy recycling systems. Biotechnology is one of the futureoriented technologies, and one that will play a major role in the exploitation of biomass energy. All biomass (plant, animal and microbial), originates through CO2 fixation by photosynthesis. Biomass utilization is consequently included in the global carbon cycle of the biosphere. Biomass energy in developing countries, originates from fuelwood, animal wastes, and agricultural residues, and is primarily utilized for activities which are essential to survival, such as cooking and obtaining water. Improvements in the living standards in

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these countries will result in the non-essential use of energy. Development of technologies that efficiently produce biomass, and convert it to more convenient forms of energy is therefore very important.

Photosynthesis and biomass Photosynthetic efficiency Photosynthesis can be simply represented by the equation: CO2 + H2O + light !’ 6 (CH2O) + O2 Approximately 114 kilocalories of free energy are stored in plant biomass for every mole of CO 2 fixed during photosynthesis. Solar radiation striking the earth on an annual basis is equivalent to 178,000 terawatts, i.e. 15,000 times that of current global energy consumption. Although photosynthetic energy capture is estimated to be ten times that of global annual energy consumption, only a small part of this solar radiation is used for photosynthesis. Approximately two thirds of the net global photosynthetic productivity worldwide is of terrestrial origin, while the remainder is produced mainly by phytoplankton (microalgae) in the oceans which cover approximately 70% of the total surface area of the earth. Since biomass originates from plant and algal photosynthesis, both terrestrial plants and microalgae are appropriate targets for scientific studies relevant to biomass energy production.

On the basis of these limitations, the theoretical maximum efficiency of solar energy conversion is approximately 11%. In practice, however, the magnitude of photosynthetic efficiency observed in the field, is further decreased by factors such as poor absorption of sunlight due to its reflection, respiration requirements of photosynthesis and the need for optimal solar radiation levels. The net result being an overall photosynthetic efficiency of between 3 and 6% of total solar radiation.

Biomass wastes and their conversion Wastes and residues currently constitute a large source of biomass (1). These include solid and liquid municipal wastes, manure, lumber and pulp mill wastes, and forest and agricultural residues. With the exception of feedstocks of low water content, most of this biomass cannot be directly utilized, and must undergo some form of transformation, prior to being utilized as a fuel. Biological processes for the conversion of biomass to fuels include ethanol fermentation by yeast or bacteria, and methane production by microbial consortia under anaerobic conditions.

Wood wastes in the paper and pulp industries and bagasse from the sugar-cane industry are examples of biomass likely to accumulate at a single site. The cellulosic nature of these biomass materials, necessitates their hydrolysis to glucose, prior to ethanol fermentation. The net energy balance for the processes involved can, however, be problematic in that energy requirements for cellulose hydrolysis and distillation, must be lower than the energy in the output ethanol.

Unlike ethanol fermentation, anaerobic digestion for methane production, utilizes organic materials containing carbohydrates, lipids, and proteins. Many species of microbes work cooperatively in an anaerobic digester, in which these polymeric materials (i.e. carbohydrates, proteins and lipids) are first decomposed to organic acids, and then to hydrogen and carbon dioxide, from which methane is synthesized by methanogens. A variety of raw materials which include agricultural wastes, municipal solid wastes, market garbage, and waste water from food and fermentation industries, are applicable as substrates for this 59

process. Waste products derived from animal husbandry are applicable to anaerobic digestion, with the added bonus of solving the environmental issues of unpleasant odors and eutrophication. Although smallscale digesters are popularly used at both the farm and village levels, large-scale operations are still in need of considerable technical improvement and cost reduction, and thus require both microbial and engineering studies.

Methane and ethanol can also be produced from cultured microalgal biomass through anaerobic digestion and microbial fermentation processes, respectively. The economics of fuel production from microalgal biomass is however largely dependent on a microalgal CO2 fixation step similar to that required for the production of H2 and algal oils.

Fuel production via microalgal CO2 fixation One of the most serious environmental problems today is that of global warming, caused primarily by the heavy use of fossil fuels. In Japan, large amounts of CO2 are released into the atmosphere from electric power plants and industry. The CO2 generated by these large point sources could potentially be recovered with relative ease through the use of an established technology such as chemical absorption. The enormity of the amounts of potentially recoverable CO2 would however necessitate the development of technologies for sequestering or, more favorably, utilizing this CO2.

Photosynthetic microalgae are potential candidates for utilizing excessive amounts of CO2, since when cultivated these organisms are capable of fixing CO2 to produce energy and chemical compounds upon exposure to sunlight. The derivation of energy from algal biomass is an attractive concept in that unlike fossil fuels, algal biomass is rather uniformly distributed over much of the earth's surface, and its utilization would make no net contribution to increasing atmospheric CO2 levels. Although algal biomass is regarded as a lowgrade energy source owing to its high moisture content, through biological processes, it may be converted to modem gaseous and liquid fuels such as hydrogen, methane, ethanol, and oils.

Hydrogen is regarded as a potential energy source of the future, since it is easily converted to electricity and bums cleanly. Hydrogen is currently produced by fossil fuel-based processes which emit large amounts of CO2, and relatively smaller amounts of other air pollutants such as sulphur dioxide and nitrogen oxides. Biological H2production has thus recently received renewed attention owing to urban air pollution and global warming concerns (2). Biological hydrogen production methodologies incorporating artificial reconstitution systems with chloroplast, ferredoxin, and hydrogenase; a heterocystous cyanobacterial system with oxygen scavengers; and an algal system in a day-and-night cycle, have been studied in Japan.

The use of microalgae as sources of liquid fuels is an attractive proposition from the point of view that microalgae are photosynthetic renewable resources, are of a high lipid content, have faster growth rates than plant cells, and are capable of growth in saline waters which are unsuitable for agriculture. While the lipid content of microalgae, on a dry cellular weight basis varies between 20 and 40 %, lipid contents as high as 85 % have been reported for certain microalgal strains. Botryococcus braunii, is a unique microalgal strain, having a long-chain hydrocarbon content of between 30 and 40% (dry weight basis), which is directly extractable to yield crude oil substitutes. Both physical and chemical processes are applicable in the production of liquid fuels from algal strains of high lipid content. These processes include direct lipid extraction in the production of diesel-oil substitutes, transesterification in the formation of ester fuels, and hydrogenation in the production of hydrocarbons (3). Oily substances are also produced via liquefaction of microalgal biomass through thermochemical reactions under conditions of high pressure and temperature.

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Microalgae as the Third Generation Biofuel Nowadays, the petrochemical resource shortage and environmental pollution are two critical challenges, which need to be addressed by our society. Since limited petroleum resources that have become increasingly depleted, petroleum oil shortages as well as rise in gasoline prices have become important factors in restricting the global economy. Furthermore, according to the results of scientific literatures, environmental pollution is caused by the huge amounts of fossil utilization, leading to global warming and disasters related to climate change. In order to solve these problems, both social and industrial researchers have started looking for renewable energy alternatives that can partially replace fossil fuel resources for establishing a more sustainable society and promoting economic recovery in the world. Biomass energy, as one of the representatives of renewable energy, has been developing rapidly in form of agriculture and aquaculture. Biomass energy is usually produced by terrestrial crops and marine algae for conversion into biofuel and biogases.

The cultivation of microalgae is the first step of the whole microalgae bioenergy production process, cultivation depend on different conditions such as climate conditions, water resources, CO2 supply and cultivation methods. These factors will directly effect on the microalgae growth. To get high quality of 2 microalgae feedstocks, cultivation techniques will be studied. After cultivation, production part will be started to research. The production technology of microalgae is one of the most difficult and complex points need to be solved, including harvesting microalgae, oil extraction and energy conversion parts. Although most of these technological methods can be used in both algae energy and crops energy extraction, the results have also some differences between marine algae and terrestrial crops, such as oil yields, land use and commercial production situations. For achieving large scale production, the critical problem is how to reduce the investment cost and production cost during the whole microalgae biofuel production. High cost input became the biggest challenge in the microalgae bioenergy development.

Following this definition these are requirements that need to be satisfied to reach a sustainable algae production:  Green Gases emission balance should be ensured during the production process.  Microalgae production cannot destroy the self cleaning capacity of local plants and soil.  Microalgae production cannot endanger the food supply.  Microalgae production does not impact on biodiversity.  Maintaining and improving local soil quality  Maintaining and improving local water resources and prohibiting excessive consumption of ground water and surface water resources  Maintaining and improving the air quality  Algae production can promote local economic and social prosperity, increasing employment opportunities.  Microalgae Production Companies should respect the benefits of employers and local peop

Concepts of Biomass Energy and Algae Biomass energy sources have three generations development steps. The first generation biofuel feedstocks derived from food crops, such as sugarcane, corn and wheat.

Rice straw and switch grass as sorts of non-food raw materials become the second generation biofuel feedstocks. The third generation biofuel feedstock is algae (especially microalgae). Algae will probably play an increasing role in the sustainable energy use field in the near future (Patil and Tran, 2008). Algae are the oldest plant living in the freshwater, saline and even sewage.

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Microalgae Microalgae refer to small size algae which shape can only be seen under the microscope. Microalgae are the main primary producers in the aquatic ecosystem (Becker, 2004). Chlorella, spirulina and Nitzschia as the main microalgae sources are usually used to produce biofuel (Chisti, 2007). They are sort of single primitive cell organism with high photosynthesis capability. The growth period is short, and the cell doubling time of microalgae is only 1-4 days. Microalgae which contain at least 30% lipids in the microalgae cell have possible to be used to convent biofuel. Through photosynthesis, microalgae can absorb large amounts of CO2 to produce sugars and oxygen. The photosynthesis reaction equation as follow: 6CO2 + 6H2O + sunlight energy →C6H12O6 (sugars) + 6O2 Then sugars can convert to lipids, proteins and carbohydrates, which are as the materials can be converted to the biofuel (Field, et al., 1998).

To sum up, the advantages of microalgae in energy production can be found in the following points: 1. Microalgae have chlorophyll and other photosynthetic organs, which can do photosynthesis. So microalgae use the sunlight, H2O which contain in the microalgae cell and CO2 from the air to convert organic compounds which can be produced to the biofuel.

2. The reproduction of microalgae is generally split type breeding, the cell cycle is relatively short, so it is easy to carry out large scale cultivation.

3. Microalgae can be cultivated in the sea water, alkaline water and even waste water, so it is the significant method to produce bioenergy in the freshwater shortage areas and barren land areas.

Cultivation Microalgae Cultivation is the first production step in the energy production system. How to produce the best quality microalgae feedstocks is the main task in the cultivation process. According to the study of characteristic and function of microalgae, some scientific microalgae cultivation methods have been concluded. At present, the cultivation methods of the microalgae production are commonly using in these two ways: The open pond system and Close photo bioreactors system.

The open pond system The open system is the oldest and the simplest way to cultivate microalgae.

In principle, microalgae samples are put in an open pond with water; through the natural photosynthesis and inorganic nutrients to make it grows. The open pond is usually designed in the shape of raceway. It has a paddle wheel to mix and cycle the algae cell.

Meanwhile, inorganic nutrients are added in the raceway. The open pond is deigned to a cycle mode, so the fresh feeds can be added from toward of the paddle wheel to the pond, and then microalgae can be harvested in the circulation process. CO2 needs to be added into water to supply microalgae growth.

Meanwhile, the pH value of the water and other physical conditions should be controlled to ensure that 90% of the CO2 can be absorbed.

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Concrete is usually used to build raceway. However, sometimes, in order to decrease the investment cost, a pit is digged on the ground by cultivation farms directly. And then a plastic liner is spread inside the pit in order to prevent soil eroded by liquid. Most of the open pond systems are shallow ponds. The size of the raceway is about 15cm-30cm deep for letting enough sunlight radiates to the microalgae pond. In the microalgae cultivation process, in order to get the ideal microalgae products, water, necessary nutrients and CO2 are necessary conditions to be supplied to the pond. At the same time, O2 has to be removed as well.

Compared with the open pond system, the close photobioreactor system has more stable culture conditions and high concentration of microalgae cultivation is easier to be carried out. The biomass productivity of close photobioreactors can average 13 times more than the open pond (Chisti, 2007). This method can be operated under sterile environment. However, the expensive investment costs are the biggest challenge of close photobioreactor system to achieve industrialization. After that, the microalgae need to be harvested from the pond or photobioreactors in further production processing.

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Microalgae oil extraction Microalgae oil extraction is the following step of harvesting. Microalgae oil remains in the microalgae cell after drying. The microalgae oil is remained in the cell by the cell wall and cell membrane for stopping the oil release from the cell. The key point of oil extraction is to break the cell wall and cell membrane, and then let the oil release from the microalgae cells. Microalgae oil can be extracted by many methods.

Chemical cool press method, Enzymatic Extraction and Supercritical Fluid Extraction are the common use methods in the microalgae oil extraction process. Chemical cool press technology is a relatively simple method in the industrial production.

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The principle is that dried microalgae feedstocks are directly pressed by mechanical machine with some chemical solvents to get microalgae oil. The function of chemical solvent (benzene, ether, and hexane) is to dissolve the cell wall in order to make oil release from microalgae cell. During the whole process, no heat energy is participation. 95% oil of the total oil content may probably be pressed from the microalgae cells using this method (Oilgae, 2013). Enzymatic Extraction refers to the use of enzyme to degrade the algae cell wall to extract oil. This method is much easier than others. Catalyst and methanol are added into the dried microalgae convert to methyl esters, which is the main content of bio-diesel. Because lipid bond of oil exist in the methyl esters, oil is extracted from the methyl esters (Mendes et al., 2003).

Supercritical fluid refers to decrease the temperature to supercritical temperature: carbon dioxide has both gas and liquid forms that co-exist in the supercritical temperature. This supercritical fluid as organic solvent is permitted into microalgae cells to extract oil. The quality of algae lipid can be protected by the supercritical fluid in the extraction process at the low temperature. This method has been used in a small scale of biodiesel extraction. However, because of high production cost, it hasn’t been applied for the large scale biofuel production so far.

Energy Conversion from microalgae to bioenergy The operating principle of microalgae energy conversion is that biomass materials are converted to biofuel energy by using chemical or biological methods. Thermochemical conversion and biochemical conversion as two main energy conversions are commonly used in the laboratory experiments and a few of industrial productions. The different kinds of bioenergy can be produced from microalgae by different techniques in the energy conversion processes. In order to understand the most suitable technical conversion method of microalgae, energy conversion must be studied. There are five commonly used techniques, which are gasification, liquefaction, pyrolysis, fermentation and transesterification. These techniques can be used to produce biogas, bio oil, biodiesel and bio ethanol from microalgae.

Thermochemical Conversion Thermochemical conversion is a technique which refers to use chemical methods to convert biomass materials to biofuel under heating condition. It includes gasification, pyrolysis and liquefaction. Gasification describes a partial non catalytic oxidation reactions at high temperature condition (approximately 800900℃) in which process the solid fuels are converted to the gas fuels. The main products include CO, H2, 65

CH4, and ammonia that are converted by the presents of nitrogen (Shie et al., 2004). However, currently in the microalgae energy conversion researches, low temperature catalytic gasification technology has been found. With this technique, biogas is extracted from microalgae with nitrogen cycling. Nitrogen cycling is a kind of recycling system along with the microalgae gasification reaction.

At the meantime, solid residues can be filtered by dichloromethane. The function of liquefaction in microalgae production is that using microalgae raw materials to produce bio-oil fuel, that can instead of petrol oil. Pyrolysis is a decomposition reaction at the high temperature without the presence of oxygen. In the microalgae energy conversion, pyrolysis is a Thermochemical process which converts biomass to biofuel.

Biomass material is combusted in the non oxygen condition up to around 500℃. Then hydrocarbon-rich gas mixture, oil fraction and high carbon content solid residue were produced (Miao et al., 2004). Slow pyrolysis process and fast pyrolysis process are two main methods of pyrolysis technology. In the fast pyrolysis process, under the effect of catalyst, high heating rate and short gas residence time, biomass can be decomposed to the short chain molecules and then all the gases will be cooled down to the liquid fuel rapidly as biofuel directly.

Because of operation theory of fast pyrolysis, fast pyrolysis process is recommended to be applied in the biofuel production (Miao et al., 2004). The reaction principle is that drying and grinding the biomass materials and then fills the materials into the reactor. After that, products flow into a cyclone for cooling and separating the final products (bio-oil, charcoal and gas).

Some of gases can be recycled to the drying step, and other gases are reflowed to the reactor to supply heat energy for the heating process. Comparing with fast pyrolysis process, slow pyrolysis process has low heating rate and long gas residence time. It will cause oil yield reduction and influence on the properties of biofuel. Currently, slow pyrolysis process has rarely been used in the biofuel production.

Biochemical Biochemical process means a process in which biochemical characteristics of biomass raw materials and the metabolism of microbial are used to produce gas fuel and liquid fuel. There are two common biochemical conversion methods can be used in the microalgae energy production as fermentation and transesterification methods.

Fermentation refers to a process that converts sugar to gases and ethanol (alcohol) in the presence of yeast catalyst. Fermentation is widely applied in producing bio ethanol by sugar crops and starch crops (McKendry, 2003). Converting biofuel from the microalgae by using fermentation method is a practical approach as well. Microalgae contain rich amount of starch, which can be converted to sugar. The 11 production procedures can be shown as the following steps. In the first step, starch is extracted from the microalgae cells with the help of an enzyme or mechanical machine.

The second step, when the microalgae cells begin to degrade, saccharomycess cerevisiae is added into the microalgae raw material for fermentation. Then ethanol and carbon dioxide will be produced.

The reaction equations are:

In the last step, liquid ethanol will be took out from the tank and pumped into another holding tank to be distilled. Carbon dioxide gas can be collected and reused for microalgae cultivation again.

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Transesterification is an exchange reaction. With the presence of catalyst, an ester reacts with an alcohol to produce a new ester and a new alcohol. The catalyst can be an acid, a base or an enzyme (biocatalyst). Since this reaction is a reversible reaction, methanol should be added as an excess amount for achieving high conversions.

Transesterification can be applied to produce biodiesel production from the microalgae. The first step is extract oil from the microalgae and then removes water from the oil by increasing temperature up to 120℃ in 5-10 min. The removing of water is because that water can lead to saponification occurs when the ester bond of triglyceride is cracked. Then the second step is mixing process, in which the oil, sodium hydroxide (NaOH) and methanol are cooled and mixed.

The transesterification reaction is:

The following step is to heat the clean oil to 60 ℃need in 5 min, and then mix c to be well mixed for about 30 mins mechanically. And after that the mixture solution will be cooled and separated in the third step. The separation process should take around 15-60 min. After then, methyl ester floating on the top lay, and glycerol at the bottom lay. The last step is to wash and dry the methyl ester (biodiesel). (Amin, 2009) The characteristics of microalgae and their production processes with different techniques have been studied. Microalgae as the Third Generation Biofuel feedstock have been detailed understanding from cultivation to bioenergy production. After that, the advantages and disadvantages of microalgae compared with other biomass feedstocks need to be analysed.

Results Comparation between microalgae and other biomass feedstocks Biofuel has been used for thousands of years. The original biofuel feedstocks are only woods and straws. They are only used for heating and cooking. With the advancement of technology, some sorts of food crops (corn, wheat) can be used to produce oil. These crops are known as the first generation Biofuel. After that, scientists found that bio ethanol and biomethane can be extracted from lignocellulosic matters as well.

Since then, the second generation biofuel appeared.

Microalgae as the raw material representative of the third generation biofuel are being recognized by people recently. Compared with The first and the second generation biofuel, what are the advantages and disadvantages of microalgae in the energy supply and energy production fields will be discussed in this section.

The First generation biofuel Food crops as the main representative of the first generation biofuel have been widely used in biofuel industrial production. The raw materials can be divided into three categories which are sugar crops

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(sugar cane and sugar beet), starch crops (corn, wheat and sorghum) and oil crops (rapeseed, soybean and sunflower). All of these feedstocks can be converted to the biofuel by different techniques.

For example, corn is one of the most common use feedstocks are widely grew in the U.S. and Brazil.

(Sims and Taylor, 2008) The main product is bio-methanol which can be applied to replace a few part of gasoline in the world currently. But the development of the first generation biofuel is restrained by some problems. Planting crops have not only a longer growing cycle, but also demands large areas of arable land.

As the first generation biofuel were produced in a large scale, so that a lot of arable land was occupied by this reason and resulting in a decreased food production problem. Therefore, solving “Energy Crisis” by food crops will increase “Food Crisis”.

The Second Generation Biofuel The second generation biofuel are using lignocelluloses crops as raw materials to produce biofuel. Lignocelluloses exist in herbaceous plants and woody plants on the Earth, as well as all timbers and other crop wastes (switch grass).

Since the production feasibility of the second generation biofuel has been tested, people hope this new biofuel feedstocks can be slowed down the food shortage and excessive land reclamation problems a bit. Even lignocelluloses feedstock can be replaced the food crops. But even if the lower the price of the second generation biofuel raw materials and high concentration of the cellulose contents are the advantages of the second generation biofuel, the production cost of second generation biofuel are much higher than the first generation biofuel. So the second generation biofuel have not been achieved commercial production yet.

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The Third Generation Biofuel The Third Generation biofuel feedstocks are aquatic microorganisms. Microalgae are leading development of the third generation biofuel. The advantages of microalgae are high carbon adsorption ability, high lipid contents, simple growth environment and short time growth. Among them, the lipid contents of microalgae are 25 to 200 times more than soybeans. (Chen, 2010) The extracted oil from microalgae can be made into biodiesel and its carbohydrate can be fermented to alcohol, as well as the nitrogen and phosphorus can be recycled as fertilizer.

Compared with terrestrial plants, microalgae can save much more arable land and fresh water sources than other biofuel feedstocks. But the first generation biofuel (corn) have been achieved through the large scale production. In the opposite, the immature production techniques of microalgae bioenergy production, unknown environment impacts, are two of the challenges, which remained to be developed, to reach large scale production 69

of microalgae biofuel.

The microalgae oil yields and land demands of different biomass are showed by these two figures below:

In these two figures, algae 50% TAG has been exampled. Algae 50% TAG means microalgae which contain 50% lipid contents and cultivating in the Close Photobioreactors system. The results of these two figures above showed that oil palm is the best feedstock of the first and second generation biofuel feedstocks, which has the highest oil yield and the lowest land use. Compared with oil palm, 50% oil content 70

of microalgae can produce at least 10 times amount of oil palm, with only 1/160 use of land area. Much lower land use and high oil yield are thus important advantages of microalgae.

Climate condition, water resources, carbon dioxide, land and nutrients are main conditions that should be satisfied on the large scale microalgae production. ● CLIMATE CONDITION Autotrophic microalgae need a low sunlight environment to be cultured.

Intensive sunlight can restrain microalgae growth, even result in microalgae cell death. The solar radiation of ca.1500 kwh/m-2 /yr is the most suitable condition for microalgae growth (Maxwell et al., 1985). Since microalgae live in the water, the air temperature has slight effect on the microalgae production. Water temperature which can be influenced by solar heating and evaporation cooling, it is important for the growth of microalgae. So once water temperature is changed by climate condition, it will take big impact on the microalgae grow rate. ● WATER RESOURCES Large amounts of water resources are needed during the microalgae production. Therefore, the low cost water source is a critical problem on the commercial production. Fresh water need to be added into the pond to cultivate microalgae and to balance water evaporation, as well as cooling the photobioreactors in the closed cultivation system. Generally, the recommended approaches are (1) using seawater or saline groundwater to culture microalgae. The coast regions have enough sea water resources which have potential possibility to cultivate microalgae on large scale production. But saline groundwater needs to be per-treatment to remove some compositions which can restrain the microalgae growth.

Therefore, microalgae are more suitable to be cultivated than terrestrial plants in water scarcity areas. ● Carbon dioxide: high concentration of CO2 is needed to produce microalgae so that CO2 enriched environment is suitable for large scale microalgae production. The microalgae production factories should be built close to high CO2 emission places like nuclear power plant, chemical industrial factories, natural gas treatment factories and ammonia production factories etc. ● Land: seawater can be used to culture microalgae at the coastal region, so less land will be used than other feedstocks. If some open ponds need establish on the terrestrial land, flat land with no more than 5% slopes could be the best choice. Otherwise, the installation of factory equipments and production cost will be influenced by land use. ● Nutrients: fertilizers are very much needed to increase microalgae growth rate, such as nitrogen, potassium and phosphorus.

Because each algae cell contains approximately 7% of nitrogen and 1% phosphorus. In small scale production, microalgae can absorb these nutrients from the water. But the amount of nutrients demand on large scale production is much more than small size production. For example, if all of the transport fuel would be replaced by microalgae fuel in the EU, it would need around 25 million tonnes of nitrogen and 4 million tonnes of phosphorus per year (Wijffels and Barbosa, 2010). In terms of present fertilizer production capacity of the EU, they will be not able to supply such a large amount of fertilizers to cultivate microalgae.

Economics of microalgae bioenergy production Another important factor beside the listed above is economic concern. It is the vital important factor in commercial scale microalgae production. Cost of capacity depends on many factors of the whole microalgae production, such as oil contents, yield of microalgae, conversion cost, transportation cost and tax etc. Currently, the cost of microalgae oil is far more expensive than one of petroleum oil. For example, Chist (2007) estimated that the price of annual output 10,000 tons of microalgae which contain 30% lipid is $2.80/ liter (equal to 10.50/gallon) exclude conversion cost, marketing cost and tax.

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Meanwhile, the petroleum price is $3.80 - $4.5 per gallon in the Virginia in the U.S. The price of microalgae oil directly relates to the petroleum oil. There is a calculation equation can explain the relationship between algae oil and petroleum oil.

The energy cost input of microalgae Energy cost analysis can be used to evaluate the cost of microalgae production system, and help to find the main factors which occupied the most percentage of the production cost. Therefore, these data can be supplied to the future technology improvement. The data are based on laboratory scale production. There are two figures with four different scenarios show the production cost from cultivation to harvesting processes. Co-products cost and waste water treatment cost were excluded in these following figure.

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Here is the life cycle perspective of microalgae, which presented “cradle to cradle� concept is applicable to microalgae production and consumption system. Microalgae are cultivated into the pond or PBRS with water, relying on sunlight, CO2 and nutrients (N, P and K) to grow. Meanwhile, O2 and excess CO2 will be released into the air. Microalgae will be transported to the next stage which is harvesting & oil extraction process. Electricity is needed to supply electric power to the machines in this stage. After harvesting, dry microalgae are produced, and then microalgae oil will be extracted from dry microalgae in the oil extraction process. Residues (algae cakes) from oil extraction can be used as co-production to sell, as well as waste water is assumed to be recycled. Bioenergy will be produced in the energy conversion process, there are some related machines consuming electricity.

Thereafter, bioenergy will be sold to the traffic tools (cars) holders. Through biofuel combustion, tail gases which contain high concentration of CO2 will be release from the traffic tools to the atmosphere. The CO2 from automobile exhaust and excess CO2 from cultivation stage combine with existing CO2 in the air can be formed to new CO2 source to feed microalgae.

The world consumption of liquid oil in the will dramatically increase in the near future, especially in non-OECD Asia. Secondly, by the end of year 2035, biofuel as a product of liquid oil will be taking a large percentage of all liquid fuels production. Microalgae as the third generation biofuel will contribute more positive energy to the energy markets in the foreseeable future.

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WAVE AND TIDAL ENERGY A Tidal power plant mainly consists of the following: 1. A barrage with gates and sluices 2. One or more basins 3. A power house A barrage is a barrier constructed across the sea to create a basin for storing water. The barrage has to withstand the pressure exerted by the water head and also should resist the shock of the waves.

A basin is the area where water is retained by the barrage. Low head reversible water turbine are installed in the barrage separating the sea from the basin.-

During high tide, water will flow from sea to tidal basin through turbine, thus producing electricity.

During low tide, water will flow from tidal basin to sea through turbine producing electricity.

The ocean, covering 70% of the Earth’s surface, produces a vast amount of mechanical energy in the form of tides and waves. With increasing prices for fossil fuels, a growing demand for electricity worldwide, and increased concern with global warming caused by carbon emissions, ocean energy may soon find a place in the energy marketplace. This paper investigates the fundamentals behind wave and tidal energy, looks at a few technologies for harvesting energy from both, as well as the economic feasibility of these methods, and finally examines the consequences of using the ocean to produce energy.

A new technology, there are a large variety of devices that could conceivably be used to produce electricity from either wave or tidal forces. As the industry evolves, these will narrow down to a select few, based on their production levels, costs, and durability. However, it seems unlikely that a single device will prevail; the optimal device is largely dependent on the environment in which it will be used.

Like solar and wind energy, there is a problem with intermittency when using wave and tidal energy.

This is a problem for communities solely dependent on these sources. It will also prove a difficulty when integrating onto the electrical grid. However, wave energy is much more constant than either solar or wind energy. There are seasonal variations, but these changes follow the energy consumption patterns: more energy is needed in the winter for heating, and this is when the power from waves is greatest. Tides are even more consistent than waves; moreover, they are completely predictable. Given the head start solar and wind technologies have had, it seems likely that any issues with intermittency will be ironed out before wave and tidal energy ever become significant energy producers.

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The environmental and social effects of both wave and tidal devices should be thoroughly considered before implementation of either type of device. While there are possible side affects from using these devices, they are largely dependent on the location of the device. As a result, each site must be analyzed separately to weigh the possible affects of an ocean energy device.

Technology There are many different methods of extracting energy from the waves and the tides. A relatively new industry, there are a large range of prototypes but very few devices are actually installed and producing electricity. In addition, many of the devices are designed specifically for a certain site, or for explicit wave and tidal conditions. While it would be expected that only some of these devices will actually prove marketable, it seems likely that wave and tidal devices will need to be specially designed to fit the ocean conditions of a given site.

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Waves Waves are produced by the transfer of energy from winds to the water. The winds are a result of solar heating. Both land and water act as solar radiation collectors, water being the more efficient of the two. When the water is warmed, it in turn heats the air above it. The warm air then rises, displacing cooler air, which descends to be heated by the water in turn. As a result, thermal air currents are generated. As these currents blow over the surface of the water, friction between the two causes the surface of the water to stretch, the result of which is small ripples, or capillary waves. This causes more surface area for interaction between the wind and water, causing more stretching, and increasingly larger waves. Waves can also be produced by seismic disturbances, resulting in tidal waves or tsunamis. While these are rare, they are still important when determining the maximum load wave energy devices must withstand.

It is estimated that all the power of waves breaking on the world’s coastline is approximately 2-3 TW. In the optimal locations for wave energy, wave energy density can average 65 MW for a single mile of coastline, or about 70 kW of power for every meter of wave crest length.1 During the winter, this number rises to 170 kW/m and can reach as high as 1 MW/m during storms.2 While wave power does vary greatly with the seasons of the year, the greatest power from the waves coincides with the greatest need. Waves have the most energy in the winter, and it is at this time that the most energy is needed for heating. For comparison, a single wind turbine can produce up to 3-MW of electricity and a standard coal-fired power plant produces on the order of 100 MW.

1

Ocean Topics. 26 Apr. 2005. U.S. Department of Energy. 22 Apr. 2005 <http://www.eere.energy.gov/RE/ ocean.html> Wave Energy: A Concentrated Form of Solar Energy. Wave Dragon. 22 Apr. 2005 <http://www.wavedragon.net/ technology/wave-energy.htm> 2

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It is important to note that, once formed, ocean waves can travel great distances without a significant loss of energy. This gives wave power a certain amount of predictability: even in periods of little wind (and therefore little wave production) waves from further away can still be counted on for energy production.

Waves have two types of energy: potential and kinetic. As a wave moves in a circular motion, water molecules are raised above the water line, resulting in potential energy. This can be exploited by using such devices as oscillating water columns and floats and pitching devices. Kinetic energy results from the circular motion of the water itself. By using wave surge or focusing devices, this kinetic energy can be utilized.

Heaving buoys Heaving buoys were originally developed for use in the military to recharge Navy robot submarines.3 These devices convert the orbital motion of surface waves into electricity. The heaving motion of the buoy drives an underwater piston and assembly that is attached o the buoy by a long rod. Figure 1 shows a diagram for AquaEnergy Group Ltd.â&#x20AC;&#x2122;s heaving buoy device, the IPS Buoy.

Figure 1: The IPS Buoy wave energy http://www.aquaenergygroup.com/home.htm

device.

The buoys have diameters ranging from 3 m up to 12 m; they can be either act as individual power stations or connected to a central generation unit. A single 10-m IPS Buoy can produce as much as 150-250 kW, for more than 1.4 GWh of electricity for a 3

Information Resources: Ocean Energy. 26 Apr. 2005. U.S. Department of Energy. 22 Apr. 2005

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year. However, this requires optimal wave power on the order of 50-70 kW/m and a minimum water depth of 30 m.4

Floats and Pitching Devices Floats, and pitching, devices bob or pitch, funneling water into a reservoir and thereby producing electricity. The Wave Dragon, manufactured by Wave Dragon ApS, is such a device. As is seen in Figure 2, the device consists of two wave reflectors that focus the waves towards the ramp where the water overtops into a reservoir. When the water enters the reservoir, the result is a height difference between the water in the reservoir and the sea level. The resulting pressure is converted into power through variable speed axial turbines located in the turbine outlet. This is a slack moored device, meaning that it needs only be attached with an anchor to the seabed in order to prevent drifting.

Figure 2: (Left) Basic diagram showing the function of the Wave Dragon. (Right) Picture of the Wave Dragon prototype being tested at the Danish Wave Energy Test Station in Nissum Bredning. http://www.wavedragon.net/technology/prototype.htm.

It is estimated that a single Wave Dragon unit will produce electricity ranging from in a 24-kW/m wave climate up to 52 GWh/year in 72-kW/m waves.5

12 GWh/year

Oscillating Water Columns Oscillating water columns generate electricity through the rise and fall of water in a cylindrical shaft.

Waves cause the water in the column to rise and fall, which then drives air in and out the top of the shaft where there is an air-driven turbine. The turbine is then forced to move, resulting in the production of energy.

4

OWEC â&#x20AC;&#x201C; Offshore Wave Energy Converters. 8 Jan. 2002. Interproject Service. 22 Apr. 2005 <http:// members.tripod.com/Interproject/presentation.htm> 5 Prototype project. Wave Dragon. 26 Apr. 2005 <http://www.wavedragon.net/technology/prototype.htm>

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The Limpet, shown in Error! Reference source not found. is located on the Isle of Islay and is the first commercial wave generator in the world. Built by the Scottish company Wavegen, this machine is an oscillating water column. The waves produce a column of water inside the device that then creates a pneumatic pressure in the air chamber above the column, causing two counter rotating turbines to turn.

Each of these turbines is linked to a generator capable of producing up to 250 kW, for a total of 500 kW.6 The Limpet was constructed to withstand the worst possible ocean conditions. Built with a higher density of steel reinforcement than a nuclear bunker, the Limpet has survived the worst storms on Islay in living memory. The extreme ocean loads predicted are probably much greater than any actual loads the Limpet will experience. Because of this, it will be possible to make major cost reductions in the next model now that a better estimate of actual ocean conditions is available.

Wave Surge Device Another wave energy device is the wave surge, or focusing device. These devices are mounted on the shore; they concentrate the waves and channel them into an elevated reservoir. Then, using traditional hydropower technologies, the water is released from the reservoir, turning turbines as it exits. These devices pose problems when building because the optimal locations are in cliffs, where the wave power is the strongest. This often requires blasting out part of the cliff to make room for the reservoir, which is an expensive endeavor. Also, access to these sites in order to install and maintain the device could prove costly.

Figure 3: Wave surge device. http://www.hawaii.gov/dbedt/ert/wavereport/wave.pdf.

Tidal Tides are primarily driven by the gravitational pull of the moon. All coastal areas get two high and two low tides in a little over 24 hours. Tidal energy is appealing in that it is completely predictable, making it much easier to incorporate onto the grid and more dependable to individual users.

6

Marine Energy â&#x20AC;&#x201C; Wave Power. 5 May 2005. Argyll & the Islands Enterprise. 22 Apr. 2005 <http://www.hie.co.uk/ aie/wave_power.html>

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The difference between low and high tides must be at least five meters â&#x20AC;&#x201C; greater than 16 ft â&#x20AC;&#x201C; for this method to harness tidal power efficiently. Unfortunately, only about forty places on earth have this necessary tidal behavior.7 Currently, cost effective power generation from tidal streams requires a mean spring peak velocity greater than 2.25 m/s, in a depth of water between 20 to 30 m.8 These restrictions also greatly limit the possibility of harnessing tidal power in much of the worldâ&#x20AC;&#x2122;s oceans. However, as technology improves these limitations are becoming less stringent.

Traditional Method Tidal power generation is much like the method used in hydroelectric plants. Gates and turbines are installed along a dam, or barrage, that stretches across the opening of a tidal basin, like a dam or estuary.

The tides then produce a different level of water on either side of the dam. When this difference is great enough, the gates open, and the water pours through, turning the turbines and thereby producing electricity. Table 1 is a summary of all the tidal energy plants that have been constructed.

7

Information Resources: Ocean Energy. 26 Apr. 2005. U.S. Department of Energy. 22 Apr. 2005. <http:// www.eere.energy.gov/consumerinfo/factsheets/nb1.html>

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Table 1: Existing tidal energy plants. http://www.poemsinc.org/papers/pontes-oeconv.pdf.

La Rance station, incorporated in a barrage across the estuary river Rance, in France, is the worldâ&#x20AC;&#x2122;s only industrial-sized tidal power station. This station, shown in Figure 4, has been in use since 1966, producing on average 240 MW of power. This is about 90% of the electricity used in Brittany. The Annapolis Royal Station in Nova Scotia is an experimental tidal power station that produces 20 MW of power from the tides of the Bay of Fundy.9

Figure 4: La Rance station. http://armorance.free.fr/barrage.htm Due to limited sites with enough tidal range for tidal barrage systems, focus has shifted from these traditional estuary barrage systems towards capturing coastal currents. Some technologies that are being developed are the tidal fence and tidal turbines.

Tidal Turbine Marine turbines are much like submerged windmills. They are optimally located in the sea where there are high tidal current velocities; the huge volumes of flowing water turn the blades of the turbines, thereby producing electricity. Unlike wind, these turbines have the major advantage of predictability: not only are tides far more constant than wind, but tidal patterns can also be calculated years in advance. Figure 9

Jones, Anthony T. â&#x20AC;&#x153;Renewable ocean energy systems becoming more viable.â&#x20AC;? Financial Times: Energy. 20 Apr. 2001.

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5 shows the 300-kW tidal turbine built by Marine Current Turbines (MCT) that was placed in he Bristol Channel in May of 2003.

Figure 5: Tidal turbine. http://www.hie.co.uk/aie/itidal_power.html.

The newest tidal turbines proposed by MCT consist of twin axial flow rotors that are about 15 m to 20 m in diameter. Each rotor drives a generator via a gearbox. The two power units of the system are mounted on either side of the center steel beam. This beam is about 3 m in diameter and is dilled into the seabed to support the turbine.10 Figure 6 shows an image of what a row of tidal turbines might look like.

Figure 6: Artistâ&#x20AC;&#x2122;s rendition of a row of tidal turbines. The second turbine is raised for maintenance. http://www.marineturbines.com/technical.htm.

10

Technology. Marine Current Turbines Ltd. 22 Apr. 2005.

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These tidal turbines have several advantages over wind turbines. First, they are much smaller. Wind turbines have a blade stretch of up to 300 ft, as opposed to the 15-ft to 30-ft diameter required for a wave device of equal production potential. In addition, the tidal turbines only have to turn about 30 revolutions per minute, about half the speed of wind turbines. These smaller sizes are possible because water has about ten times the density as air, and therefore has a higher energy density. Moreover, tidal turbines can be made from steel rather than the costly lightweight materials used for building wind turbines. Finally, tidal turbines are powered by a much more predictable source than wind turbines.11

Oscillating Hydrofoil The principles and technology regarding the oscillating hydrofoil is considerably different from the more commonly used rotational devices. The relative motion of the tidal current over the foil section causes a pressure difference on the foil section, which oscillates the hydrofoil inducing hydrodynamic lift and drag forces. The forces induce a tangential resultant force to the fixing arm of the hydrofoil that drives a reciprocating hydraulic ram pump which forces hydraulic fluid under high pressure to rotate a hydraulic motor and electrical generator. Depending on the negative or positive angle of attack relative to the stream flow, the hydrofoil will rise and fall producing the oscillating motion. The rate of oscillation depends on a number of mechanical and hydrodynamic variables. The lift generated is dependant on the velocity and density of the flow, the surface area of the foil, its aspect ratio and its profile characteristics, such as drag and lift coefficients for the optimum angle of attack.

Unlike the more conventional technologies utilising rotors, which have a constant rotational speed and linear velocity, the lift causing oscillation of the hydrofoil approximates a sinusoidal decay from the vertical to horizontal arm positions. This loss in momentum and nonlinear velocity means there is a large degree of mechanical complexity in optimising the devices power output.

Figure 7 - Blue Energy's VAOT

The angle of attack of the hydrofoil is relative to the velocity of the flow and as the hydrofoil is continually in motion, the angle of attack must be controlled to maintain efficient performance. This is controlled by program logic control (PLC), which constantly monitors all the mechanism parameters, the arm position, the flow velocity and the pressure of the hydraulic system. Using this information, the PLC controls the angle of attack of the hydrofoil through a hydraulic ram. It is important that the hydrofoil be held stably at its optimum angle of attack as if it tends to wobble, lift is significantly reduced and drag is increased, causing the overall cycle time to decrease. The power extraction also needs to be monitored as the resultant power curve is not steady, adding yet another element of complication and of course, cost.

11

Johnson, Jeff. â&#x20AC;&#x153;Power From Moving Waterâ&#x20AC;?. C&EN.82.40. 4 Oct. 2004. >

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Potential While there are many innovative ideas for harnessing the energy from the waves and tides, the question of feasibility must still be posed. The device must produce enough energy to be competitive in an energy market still dominated by cheap fossil fuel. Moreover, while there is a massive amount of energy present in the waves and tides of the worldâ&#x20AC;&#x2122;s oceans, there are relatively few places with concentrated enough ocean energy to warrant installation of energy devices.

Another major opposition to ocean energy is the ocean itself. The best places for tidal and wave power devices are in the roughest waters. Many fledgling technologies have been torn apart when actually placed in the sea. Therefore, wave and tidal energy devices must be built to withstand the worst the ocean can produce. This requires extensive studying to determine necessary durability as well as major investment in structures and material that can withstand these loads.

Figure 8 shows a world map marked with the average wave energy along coastlines. It is evident from this map that there are relatively few locations worldwide suitable for wave energy devices given 85

current technologies. Given current technology, wave energy is only feasible as an energy source for a few areas of the world: mainly Europe, parts of Australia, the southern most part of South America, and the northern reaches of North America.

Figure 8: This map shows the average energy for waves along coastlines. The values given are in kW per meter of wave.

In the USA, there are only five states with good tidal flows and eight with strong enough waves to warrant ocean energy devices.12 With such limited possibility in the US on a national level, it seems unlikely that Congress would support ocean energy projects for this handful of states. Only a single company has received funding from the federal government for ocean energy technologies: $12 million was given to the US Navy for pilot buoy projects offshore of Hawaii. Nevertheless, small ocean energy projects have already begun in Massachusetts, New York, Rhode Island, Hawaii, Washington, and California. In San Francisco, the board of supervisors has called for 150 kW of tidal power by January 2006.

European Union (EU) officials estimate that by 2010, ocean energy sources will generate more than 950 MW. This is enough to power for a million homes in industrialized world. Between the islands of Jura and Scarba here is the Argyll’s whirlpool which could produce up to 2 GW of electricity if harnessed using tidal devices.13 Of course resources like this are extremely rare and the devices used would need to be specially designed to obtain the maximum amount of power.

Economics The cost of ocean energy devices depends largely on three factors: 1) the magnitude and dependability of the wave or tidal resource 2) the cost of construction and maintenance of the conversion system 3) energy transmission from the site to the user

12

Johnson, Jeff. “Power From Moving Water”. C&EN.82.40. 4 Oct. 2004. <http://pubs.acs.org/cen/coverstory/8240/ print/8240energy.html> 13 Marine Energy – Tidal Power. 5 May 2005. Argyll & the Islands Enterprise. 22 Apr. 2005 <http://www.hie.co.uk/ aie/tidal_power.html>

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It is necessary to find a balance between the acceptable risk that a larger than average storm will damage the device versus the increased cost to make sure the device is strong enough to withstand such a storm. Some possible solutions to the problem of storms is intentionally sinking the device, towing it to shelter, or raising it out of the water onto the deck of a boat for the duration of the storm. Obviously, these would only work for unattached devices, such as floating buoys. For larger, secured devices, they must be built to withstand the ocean at its strongest.

It would be economical to create joint ventures between wave or tidal plants and other offshore devices. For instance, it would be possible to install wave turbines beneath offshore wind farms. Since the windiest places often have the largest waves, this would allow optimal working conditions for both technologies. Another possibility under consideration is using tidal fences as bridges.

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Even with these improvements, however, it seems most likely that ocean energy devices will be economically competitive in areas that are far away from a common electrical grid, such as remote islands or ocean facilities as long as traditional fossil fuels such as coal and oil are available.

Consequences As a renewable energy source, ocean energy has the advantage of reducing societyâ&#x20AC;&#x2122;s dependence on fossil fuels. It is a clean source of energy â&#x20AC;&#x201C; it produces no liquid or solid pollution â&#x20AC;&#x201C; and free beyond initial capital cost and maintenance. However, there are several environmental and social impacts of this device that must be considered.

Emmisions Table 2 shows an example of the total emissions that might be expected from a standard wave energy device.

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Table 2: Example of emissions for wave energy device. http://europa.eu.int/comm/energy_transport/atlas/htmlu/wavenv.html.

While these numbers would be expected to vary for different technologies, as a whole the devices would produce no emissions beyond those required for their construction. Most devices designed today use water hydraulics in order to eliminate the risk of oil spills inherent in standard hydraulic systems.

Observably, these devices provide a much cleaner source of energy than any of the fossil fuel technologies, and even some renewable sources.

Ecological Effects One of the biggest concerns with both wave and tidal energy is the impact they have on the ecology.

However, the full effect that slight alterations of tides or wave patterns on an ecosystem is unknown; it will most likely remain that way until devices are installed and the effect can be observed. The La Rance barrage did change the local tide patterns slightly and any environmental impact was negligible. Unfortunately, this would probably not be the case for all such installations. Since the barrage separates the ocean from the water entering the estuary, the salinity in the estuary would be reduced. Moreover, the tides and within the basin are reduced by about half.

The result is a change in water quality, sediment movement, and composition of the bed sediments. This in turn would affect the organisms that live in the water, which could result in an overall change in coastal animal habitats.

On the other hand, it is theorized that such tidal barrages could provide protection against coastal flooding during very high tides, and work as a storm barrier. Despite this potential benefit, the focus has now turned to smaller wave and tidal devices in the belief that they will have a much smaller affect on the environment. The environmental impacts are largely dependent on sites and the research necessary to analyze each individually is daunting. By using smaller scale devices, it should be possible to avoid many of these environmental concerns.

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Affect on wildlife Interestingly, it seems that many wave and tidal devices would actually stimulate marine life.

Floating devices could provide shelter to both fish and birds; since such devices would impede fishing boats, they would develop into a natural sanctuary. With an increase in fish, bird populations would prosper as well.

Currently there is actually a high demand for artificial reef structures in order to stimulate marine life. In 2000, New Jersey purchased over fifty subway cars to sink just offshore to stimulate fish populations.14 Furthermore, these structures provide not only an artificial reef environment, they are also avoided by large fishing boats; their nets and fishing gear might get caught or broken by the devices. If there is already a need for offshore structures, it seems a logical step to have those structures produce electricity as well.

On the other hand, tidal fences and tidal barrages can impede sea life migration.

Tidal turbines and most wave power devices are less environmentally damaging because they do not block migratory paths. For all of these technologies, it is important to pick sites where environmental impact will be minimized.

Another drawback of devices such as tidal turbines is their rotating blades. However, on average th

e blades rotate from around 10 to 0 rpm. In comparison, a ship propeller typically runs over an order of 14

Clark, Peter, Klossner, Rebecca, and Kologe, Lauren. â&#x20AC;&#x153;Tidal Energyâ&#x20AC;?. 13 Nov 2003. 22 Apr. 2005 <http://www.ems.psu.edu/~elsworth/courses/cause2003/finalprojects/canutepaper.pdf>

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magnitude faster than this.15 Furthermore, the tidal turbine is stationary, whereas many ships can move faster than sea creatures can swim. In this instance, ocean energy devices are less risk to marine life than the multitude of boats already navigating the seas.

Boat Traffic Ocean energy devices could be obstacles to marine traffic and may become burdensome if employed in such quantity as to impede marine travel. This would especially be difficult for fishing boats, which would have to avoid areas with wave or tidal devices. It could also be a problem for areas with significant ocean recreation and tourism. These devices, while obstacles, should not prove hazardous given modern navigation tools such as radar warning devices.

Visual Impact A major concern for all wave and tidal energy devices is aesthetic. In general, any obstruction to a view, especially an ocean view, is met with major opposition from residents. This is true not just for ocean devices, but for wind as well. However, most offshore ocean devices are not readily visible from the shore; they barely rise above the sea level and more often than not are obscured by waves. They are especially low profile when compared to oilrigs or offshore wind farms. Coastal devices, on the other hand, are visible from the shore. In this case, the advantage of having a clean, efficient energy source must be balanced with the visual impact.

Conclusion Already, wave energy is becoming economic in niche markets, mainly in places far from the grid or on offshore facilities. As the technology improves, traditional sources of energy become more costly and environmentally suspect, and a successful track record is established by installed ocean energy technologies, wave and tidal energy may become a more commonly exploited resource.

Sure enough, people have learned how to harness the power of the ocean. The ocean is a very destructive medium in which to place any device but centuries of building ships, piers, and other oceanbased structures has given people the knowledge necessary to build strong, lasting ocean energy devices.

Nevertheless, like many other renewable energy sources, ocean energy will unlikely to be economically competitive with traditional fossil fuels except for isolated communities that are far away from the grid.

Even as the technologies become more developed and commercially viable, utilizing ocean energy will still be limited to such locations that have a significant amount of tidal or wave activity.

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Clark, Peter, Klossner, Rebecca, and Kologe, Lauren. â&#x20AC;&#x153;Tidal Energyâ&#x20AC;?. 13 Nov 2003. 22 Apr. 2005 <http://www.ems.psu.edu/~elsworth/courses/cause2003/finalprojects/canutepaper.pdf>

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GEOTHERMAL ENERGY Geothermal power plants derive energy from the heat of the earth’s interior. The average increase in temperature with depth of the earth is 10C for every 30-40m. At a depth of 10-15km, the earth’s interior is as hot as 1000-12000C. In certain areas of our planet, the underground heat has raised the temperature of water to over 2000C which bursts out as hot steam through the cracks in the earth’s crust. These are called thermal springs. This steam can be utilized for power production.

What is geothermal energy?

The word geothermal comes from the Greek words geo (earth) and therme (heat). Geothermal energy is heat from within the earth. We can recover this heat as steam or as hot water and use it to heat buildings or to generate electricity. Geothermal energy is a renewable energy source because the heat is continuously produced inside the earth.

Most geothermal resources are near tectonic plate boundaries The most active geothermal resources are usually found along major tectonic plate boundaries where earthquakes and volcanoes are located. When magma comes near the earth's surface, it heats ground water trapped in porous rock or water running along fractured rock surfaces and faults. Hydrothermal features have two common ingredients, water (hydro) and heat (thermal).

GEOTHERMAL SOURCES 93

The following five general categories of geothermal sources have been identified: 1. Hydrothermal convective systems (i) Vapor dominated or dry steam fields (ii) Liquid dominated or wet steam fields (iii) Hot water fields 2. Geo-pressure resources 3. Petrothermal or hot dry rocks 4. Magma resources 5. Volcanoes The hydro thermal convective systems are best resources for geothermal energy exploitation at present.

Hot dry rock is also being considered.

TYPES OF GEOTHERMAL POWER PLANTS There are three basic types of geothermal power plants: ď&#x201A;ˇ

DRY STEAM PLANTS use steam directly from a geothermal reservoir to turn generator turbines. The first geothermal power plant was built in 1904 in Tuscany, Italy, where natural steam erupted from the earth.

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 

FLASH STEAM PLANTS take high-pressure hot water from deep inside the earth and convert it to steam to drive generator turbines. When the steam cools, it condenses to water and is injected back into the ground to be used again. Most geothermal power plants are flash steam plants.

BINARY CYCLE POWER PLANTS transfer the heat from geothermal hot water to another liquid. The heat causes the second liquid to turn to steam, which is used to drive a generator turbine.

The differences between dry steam, flash steam, and binary cycle power plants are shown in the diagrams below.

Geothermal wells are drilled at suitable locations. Water vaporized into steam comes out of the earth’s surface in a dry condition at around 200C and 8 bar. The moisture is removed by a centrifugal separator and this steam will run the turbine coupled with a generator. Steam is condensed in a condenser and re injected back into the ground by a rejection well.

Geothermal - generated electricity was first produced in Larderello, Italy, in 1904.

Currently just over 1 GW geothermal electric power (of which 0.95 GW operational) is in use in the EU, 95

producing roughly 7 000 GWh of electricity per year. With regards to the heat sector (direct and indirect use), EU installed capacity is almost 9 GWth, accounting for an annual heat production of 85 PJ. The geothermal market is currently concentrated in a number of countries across Europe, with Italy, France, Portugal, Iceland and Turkey leading the electricity sector, and Sweden, Italy, Greece, France, Germany, Hungary, Turkey, Iceland and Switzerland leading the heating sector.

Specifically regarding EGS, R&D research conducted over the past 30 years has led to the 2007 commissioning of the first EGS-assisted operating plant in Landau, Germany, and the plant at Soultz-sousForĂŞts, France which should be completed within the next two years. Nevertheless, the relevant resources are far from being fully exploited.

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According to the IEA, geothermal power plants grew worldwide at a broadly constant rate of about 200 MW/year from 1980 to 2005. In 2007 the total capacity reached around 10 GW, generating 56TWh/year of electricity.

Projections Enhanced geothermal system technologies (EGS) have the potential to cost-effectively produce large amounts of electricity almost anywhere in the world. Several pilot projects are at the moment being conducted in United States, Australia and Europe.

According to the Commission's forecast, the capacity of the geothermal power sector is expected to reach 1 GW in 2020 and 1.3 GW in 2030. The estimated maximum potential for geothermal power in the EU-27 is up to 6 GW by 2020 and 8 GW by 2030. This represents about 1% and 1.3% of projected EU gross electricity consumption by 2020 and 2030 respectively. In the heating sector, the estimated maximum potential for geothermal is up to 40 GW by 2020 and 70 GW by 2030 (direct and indirect use combined).

However, the level of market opportunity for the EU industry in emerging and developing countries remains unclear. The geothermal sector is expected to grow, especially in South East Asia and Latin America, but it is unclear by how much.

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Hurdles to be overcome by research Successful development of EGS is currently one of the major challenges facing the geothermal community.

Exploration, well-drilling and plant construction make up a large share of the overall costs of geothermal electricity.

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Drilling costs can account for as much as one third to one half of the total cost of a geothermal project.

Capital costs are closely related to the characteristics of the local resource system and reservoir. Generation costs depend on a number of factors, but particularly on the temperature of the geothermal fluid.

Geothermal energy carries a relatively high commercial risk because of the uncertainties involved in identifying and developing reservoirs that can sustain long term fluid and heat flow.

To accelerate the exploitation of geothermal resources and enhance its attractiveness to investors, several technical issues need further research.

Geothermal reservoirs are naturally occurring areas of hydrothermal resources. These reservoirs are deep underground and are largely undetectable above ground. ď&#x201A;ˇ ď&#x201A;ˇ ď&#x201A;ˇ

Geothermal energy finds its way to the earth's surface in three ways: Volcanoes and fumaroles (holes where volcanic gases are released) Hot springs Geysers

Most geothermal resources are near tectonic plate boundaries The most active geothermal resources are usually found along major tectonic plate boundaries where earthquakes and volcanoes are located. One of the most active geothermal areas in the world is called the Ring of Fire. This area encircles the Pacific Ocean.

When magma comes near the earth's surface, it heats ground water trapped in porous rock or water running

along fractured rock surfaces and faults. Hydrothermal features have two common ingredients, water (hydro) and heat (thermal).

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Geologists use various methods to find geothermal reservoirs. Drilling a well and testing the temperature deep underground is the most reliable method for locating a geothermal reservoir.

Geothermal heat pumps use the earth's constant temperatures for heating and cooling Although temperatures above ground change depending on time of day and season, temperatures 10 feet below the earth's surface are consistently between 50°F and 60°F. For most areas, this means soil temperatures are usually warmer than the air in winter and cooler than the air in summer. Geothermal heat pumps use the earth's constant temperature to heat and cool buildings. Geothermal heat pumps transfer heat from the ground (or water) into buildings during the winter and reverse the process in the summer.

A type of geothermal heat pump system

Source: U.S. Department of Energy, Office of Energy Efficiency & Renewable Energy (public domain)

Geothermal heat pumps are energy efficient and cost effective According to the U.S. Environmental Protection Agency (EPA), geothermal heat pumps are the most energy efficient, environmentally clean, and cost effective systems for heating and cooling buildings. All types of buildings, including homes, office buildings, schools, and hospitals, can use geothermal heat pumps.

The environmental effects of geothermal energy depend on how geothermal energy is used or on how it is

converted to useful energy. Direct use applications and geothermal heat pumps have almost no negative effects on the environment. In fact, they can have a positive effect by reducing the use of energy sources that have negative effects on the environment.

Source: Stock photography (copyrighted)

Geothermal power plants have low emission levels Geothermal power plants do not burn fuel to generate electricity, so the levels of air pollutants they emit are low. Geothermal power plants emit 97% less acid raincausing sulfur compounds and about 99% less carbon dioxide than fossil fuel power plants of similar size.

Geothermal power plants use scrubbers to remove the hydrogen sulfide naturally found in geothermal reservoirs. Geothermal power plants inject the geothermal steam and water that they use back into the earth. This recycling helps to renew the geothermal resource.

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How a Geothermal Power Plant Generates Electricity There is currently only 10,715 MW geothermal power installed across 24 different countries (May 2010), just a tiny fraction of the World’s consumption of electricity. The upper estimate of our geothermal resources reveals that the total potential is more than adequate to supply humanity with energy.

There are several different main types of geothermal plants:   

Dry steam Flash steam Binary cycle

What these types of geothermal power plants all have in common is that they use steam turbines to generate electricity. This approach is very similar to other thermal power plants using other sources of energy than geothermal.

Water or working fluid is heated (or used directly incase of geothermal dry steam power plants), and then sent through a steam turbine where the thermal energy (heat) is converted to electricity with a generator through a phenomenon called electromagnetic induction. The next step in the cycle is cooling the fluid and sending it back to the heat source.

Water that has been seeping into the underground over time has gained heat energy from the geothermal reservoirs. There no need for additional heating, as you would expect with other thermal power plants. Heating boilers are not present in geothermal steam power plants and no heating fuel is used.

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Production wells (red on the illustrations) are used to lead hot water/steam from the reservoirs and into the power plant.

Rock catchers are in place to make sure that only hot fluids is sent to the turbine. Rocks can cause great damage to steam turbines.

Injection wells (blue on the illustrations) ensure that the water that is drawn up from the production wells returns to the geothermal reservoir where it regains the thermal energy (heat) that we have used to generate electricity.

Depending on the state of the water (liquid or vapor) and its temperature, different types of power plants are used for different geothermal reservoirs. Most geothermal power plants extract water, in its vapor or liquid form, from the reservoirs somewhere in the temperature-range 100-320°C (220-600°F).

Geothermal Dry Steam Power Plants This type of geothermal power plant was named dry steam since water water that is extracted from the underground reservoirs has to be in its gaseous form (water-vapor).

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Geothermal steam of at least 150°C (300°F) is extracted from the reservoirs through the production wells (as we would do with all geothermal power plant types), but is then sent directly to the turbine. Geothermal reservoirs that can be exploited by geothermal dry steam power plants are rare.

Dry steam is the oldest geothermal power plant type. The first one was constructed in Larderello, Italy, in 1904. The Geysers, 22 geothermal power plants located in California, is the only example of geothermal dry steam power plants in the United States.

Geothermal Flash Steam Power Plants Geothermal flash steam power plants uses water at temperatures of at least 182°C (360°F). The term flash steam refers the process where high-pressure hot water is flashed (vaporized) into steam inside a flash tank by lowering the pressure. This steam is then used to drive around turbines.

Flash steam is today’s most common power plant type. The first geothermal power plant that used flash steam technology was the Wairakei Power station in New Zealand, which was built already in 1958:

Geothermal Binary Cycle Power Plants The binary cycle power plant has one major advantage over flash steam and dry steam power plants: The water-temperature can be as low as 57°C (135°F).

By using a working fluid (binary fluid) with a much lower boiling temperature than water, thermal energy in the reservoir water flashes the working fluid into steam, which then is used to generate electricity with the turbine. The water coming from the geothermal reservoirs through the production wells is never in direct contact with the working fluid. After the some of its thermal energy is transferred to the working fluid with a heat exchanger, the water is sent back to the reservoir through the injection wells where it regains it’s thermal energy.

These power plants have a thermal efficiency rate of only 10-13%. However, geothermal binary cycle power plants enable us, through lowering temperature requirements, to harness geothermal energy from reservoirs that with a dry- or a flash steam power plant wouldn’t be possible.

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First successful geothermal binary cycle project took place in Russia in 1967.

Cogeneration (Combined Heat and Power) Depending on what type of geothermal power plant, location and various other factors, the thermal efficiency rate is not more than 10-23%. Technically, low efficiency rates do not affect operational costs of a geothermal power plant, as it would with power plants that are reliant on fuels to heat a working fluid.

Electricity generation does suffer from low thermal efficiency rates, but the byproducts, exhaust heat and warm water, have many useful purposes. By not only generating power, but also taking advantage of the thermal energy in the byproducts, overall energy efficiency increases. This is what we call geothermal cogeneration or combined heat and power (CHP).

Here are some good examples of this:        

District heating Greenhouses Timber mills Hot springs and bathing facilities Agriculture Snow and ice melting Desalination (processes that remove salt and other minerals from saline water) Various other industrial processes

How is geothermal energy transported? It is not a surprise that the electricity that is generated with geothermal power plants is transported in the same way as you would with any other power plant (or a wind or solar farm for that matter): Voltage is increased to minimize losses and the current is sent onto the electrical grid. Transporting heat over long distances, as you would with CHP, requires a heavily insulated piping system, which is a significant addition to costs.

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The top 10 biggest geothermal power plants in the world Philippines is home to three of the 10 biggest geothermal power plant installations in the world, followed by the US and Indonesia with two each, and Italy, Mexico and Iceland with one each. Powertechnology.com lists the 10 biggest geothermal power plant installations in the world based on net capacity.

The Geysers Geothermal Complex, California, United States of America The Geysers Geothermal Complex located about 121km north of San Francisco, California, is comprised of 18 power plants making it the biggest geothermal installation in the world. The complex has an installed capacity of 1,517MW and active production capacity of 900MW. Calpine owns 15 power plants in the complex, with a combined net generating capacity of about 725MW, while two power plants are jointly owned by Northern California Power Agency and Silicon Valley Power, plus US Renewables Group, which owns the Bottle Rock Power plant. Ram Power is constructing a new 26MW geothermal power plant at the complex.

The complex covers an area of approximately 78km². Production from the geothermal field commenced in 1960 and reached its peak in the 1980s. The turbine suppliers for the power plants in the complex include Toshiba and Mitsubishi Steam.

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Larderello Geothermal Complex, Italy Larderello Geothermal Complex, comprising of 34 plants with a total net capacity of 769MW, is the second biggest geothermal power plant in the world. The power produced from the geothermal field, located in Tuscany, Central Italy, accounts for ten percent of all geothermal energy produced worldwide and caters for 26.5% of regional power needs.

Enel Green Power owns the power plants at the complex serving approximately two million families, 8,700 residential and business customers and 25 hectares of greenhouses. Reservoir depths at the geothermal field range from 700m to 4,000m below the surface. The first plant at the geothermal field was commissioned a century ago, in 1913, making it the first of its kind in the world.

The first Larderello power plant had a generating capacity of 250kW comprising of a turbine designed and built by Tosi Electromechanical Company. The geothermal plants at the field were rebuilt after they were destroyed during World War II.

Cerro Prieto Geothermal Power Station, Mexico At 720MW, Cerro Prieto Geothermal Power Station in south Mexicali, Baja California in north Mexico, is the second third geothermal plant in the world.

The power plant, like all other geothermal fields in Mexico, is owned and operated by the Comisiรณn Federal de Electricidad (CFE). The power station features four plants, comprising of 13 units. The first plant was commissioned in 1973, while the fourth plant was commissioned in 2000.

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The turbines at the complex include four 110MW condensing type, four 110MW double-flash type, four single-flash of 37.5MW each, four single-flash of 25MW each and one 30MW single-flash. They were supplied by Toshiba and Mitsubishi Heavy Industries. A fifth plant, which will comprise of two 50MW turbines, is currently under construction.

Makban Geothermal Complex, Philippines Makban Geothermal Power Complex, also known as Makiling-Banahaw Power Plants, is located in the municipalities of Bay and Calauan in the Laguna province and Santo Tomas, in the Batangas province.

It is the fourth biggest geothermal power facility in the world, with an output capacity of 458MW. The geothermal power complex is owned by AP Renewables, a wholly-owned subsidiary of Aboitiz Power. The complex consists of six power plants comprising of 10 units, including a binary plant with five 3MW units and one 0.73MW unit.

The complex, covering an area of 700ha, commenced operations in 1979. Mitsubishi Heavy Industries was one of the turbine suppliers for the plants at the complex.

CalEnergy Generation's Salton Sea Geothermal Plants, United States CalEnergy Generation's Salton Sea Geothermal Plants include a cluster of 10 generating geothermal plants in Calipatria, near the Salton Sea in Southern California's Imperial Valley. With a combined generating capacity of 340MW, it is the fifth largest geothermal facility in the world.

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CalEnergy Generation, the operator of the field, has a 50% interest in the facilities, while the remaining 50% is held by MidAmerican Geothermal. The generated power is supplied to Southern California Edison Company.

Unit 1 with an output capacity of 10MW was the first to come online in 1982. It was built by a joint venture comprising of Union Oil Company and Southern California Edison. The 10th field came online in 2000. CalEnergy Generation is currently developing new projects in the area, including the Black Rock Project, which will consist of three new 50MW geothermal plants.

Hellisheidi Geothermal Power Plant, Iceland Hellisheidi geothermal power plant is a flash steam, combined heat and power plant (CHP) located at Mount Hengill, approximately 20km east of the capital city of Reykjavik. The plant has a production capacity of 303MW of electric energy and 400MW of thermal energy.

The sixth largest geothermal power plant is owned by Orkuveita Reykjavikur. It was constructed by Mannvit Engineering and VerkĂ­s Engineering. Power generated from the plant is supplied primarily to the nearby aluminum refineries.

The power plant was commissioned in five phases from 2006-2011. It covers an area of approximately 13,000m². Six high pressure (HP) turbines for the plant were supplied by Mitsubishi, while a low pressure (LP) turbine was supplied by Toshiba.

Tiwi Geothermal Complex, Philippines Tiwi Geothermal Complex is located at Tiwi in the province of Albay, about 300km south-east of Manila. The 289MW (net) complex is the seventh biggest geothermal facility in the world.

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The Tiwi complex is owned by Aboitiz Power's subsidiary AP Renewables. It comprises of three power plants featuring two units each. Drilling works at the geothermal field commenced in 1972 and the power plant became operational in 1979.

The project was developed by National Power Corporation and Philippine Geothermal. Mitsui and F.F. Cruz were the construction contractors. The power plants use Toshiba generator units.

Malitbog Geothermal Power Station, Philippines The 232.5MW Malitbog Geothermal Power Station, located approximately 25km north of Ormoc City in Leyte Island, is the eighth biggest geothermal power plant in the world.

The plant was earlier owned by Visayas Geothermal Power Company (VGPC), which later transferred the ownership rights to Philippine National Oil-Energy Development Company (PNOC). The plant is currently owned by Energy Development Corporation. Power from the field is supplied to the Luzon Island.

The Malitbog geothermal power plant construction commenced in 1993 and was completed in 1996. It was built by Sumitomo Corporation and Fuji Electric. The plant features three 77.5MW single-cylinder double flow condensing turbines supplied by Fiji Electric.

Wayang Windu Geothermal Power Plant, Indonesia Wayang Windu Geothermal Power Plant is located in Pangalengan, approximately 40km south of Bandung City in the province of West Java. The geothermal plant, with an output capacity of 227MW, is the ninth biggest in the world.

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Magma Nusantara Limited (MNL), a wholly-owned subsidiary of Star Energy, operates the field. The engineering services for the first two units were provided by Aecom. Major contractors involved in the plant's construction included Sumitomo Corporation, Fuji Electric and Rekayasa Industri.

The first unit of the power plant started operation in 2000. It is comprised of an 110MW turbine supplied by Fuji Electric. The second unit, featuring a 117MW turbine, was commissioned in 2009. The third unit, with a generation capacity of 127MW, is expected to be commissioned in mid-2014.

Darajat Power Station, Indonesia Darajat Power Station is located at Garut in Pasirwangi District, West Java. It is the tenth biggest geothermal plant in the world, with an installed capacity of 259MW. It is managed by Darajat GPP Amoseas Indonesia, a subsidiary of Chevron Texaco.

The power station comprises of three plants serving the provinces of Java and Bali. The plants were commissioned respectively in 1994, 2000 and 2007. Plants II and III share common facilities, including the steam gathering system.

The latest commissioned plant was built by Thiess Contractors Indonesia in collaboration with Kanematsu Corporation. It features a turbine supplied by Mitsubishi Heavy Industries (MHI). The turbine for the second plant was also supplied by MHI. Hyundai Engineering supplied the equipments for the first two plants.

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OCEAN THERMAL ENERGY CONVERSION OTEC uses the temperature difference of the sea water at different depths to generate electricity OTEC utilizes the temperature difference that exists between the surface waters heated by the sun and the colder deep (up to 1000m) waters to run a heat engine. This source and sink provides a temperature difference of 20ď&#x201A;°C in ocean areas within 20 of the equator.

These conditions exist in tropical coastal areas, roughly between the tropic of Capricorn and the tropic of cancer. Such a small temperature difference makes energy extraction difficult and expensive. Hence, typically OTEC systems have an overall efficiency of only 1 to 3%. The OTEC is shown in fig.

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Ocean thermal energy conversion (OTEC) uses the temperature difference between cooler deep and warmer shallow or surface seawaters to run a heat engine and produce useful work, usually in the form of electricity.

OTEC is a base load electricity generation system.

Among ocean energy sources, OTEC is one of the continuously available renewable energy resources that could contribute to base-load power supply.[1] The resource potential for OTEC is considered to be much larger than for other ocean energy forms [World Energy Council, 2000]. Up to 88,000 TWh/yr of power could be generated from OTEC without affecting the oceanâ&#x20AC;&#x2122;s thermal structure [Pelc and Fujita, 2002].

Systems may be either closed-cycle or open-cycle. Closed-cycle OTEC uses working fluids that are typically thought of as refrigerants such as ammonia or R-134a. These fluids have low boiling points, and are therefore suitable for powering the systemâ&#x20AC;&#x2122;s generator to generate electricity. The most commonly used heat cycle for OTEC to date is the Rankine cycle, using a low-pressure turbine. Open-cycle engines use vapour from the seawater itself as the working fluid.

OTEC can also supply quantities of cold water as a by-product. This can be used for air conditioning and refrigeration and the nutrient-rich deep ocean water can feed biological technologies. Another by-product is fresh water distilled from the sea

Currently operating OTEC plants In March 2013, Saga University with various Japanese industries completed the installation of a new OTEC plant. Okinawa Prefecture announced the start of the OTEC operation testing at Kume Island on April 15, 2013. The main aim is to prove the validity of computer models and demonstrate OTEC to the public. The testing and research will be conducted with the support of Saga University until the end of FY 2016. IHI Plant Construction Co. Ltd, Yokogawa Electric Corporation, and Xenesys Inc were entrusted with constructing the 100 kilowatt class plant within the grounds of the Okinawa Prefecture Deep Sea Water Research Center. The 112

location was specifically chosen in order to utilize existing deep seawater and surface seawater intake pipes installed for the research center in 2000. The pipe is used for the intake of deep sea water for research, fishery, and agricultural use. The plant consists of two units; one includes the 50 kW generator while the second unit is used for component testing and optimization. The OTEC facility and deep seawater research center are open to free public tours by appointment in English and Japanese. Currently, this is the only fully operational OTEC plant in the world.

In 2011, Makai Ocean Engineering completed a heat exchanger test facility at NELHA. Used to test a variety of heat exchange technologies for use in OTEC, Makai has received funding to install a 105 kW turbine.

Installation will make this facility the largest operational OTEC facility, though the record for largest power will remain with the Open Cycle plant also developed in Hawaii.

In July 2014, DCNS group partnered with Akuo Energy announced NER 300 funding for their NEMO project. If successful, the 16MW gross 10MW net offshore plant will be the largest OTEC facility to date. DCNS plans to have NEMO operational by 2020.

An ocean thermal energy conversion power plant built by Makai Ocean Engineering went operational in Hawaii in August 2015 . The governor of Hawaii, David Ige, "flipped the switch" to activate the plant. This is the first true closed-cycle ocean Thermal Energy Conversion (OTEC) plant to be connected to a U.S. electrical grid . It is a demo plant capable of generating 105 kilowatts, enough to power about 120 homes

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OTEC projects around the world

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ENERGY Energy is the capacity to do work. A plenty of energy is needed to sustain industrial growth and agricultural production.

SOLAR ENERGY ADVANTAGES 1.

2.

3.

4.

Renewable source of energy Pollution free After the capital cost, the cost of power generation is quite low Wide range of applications, powering street lights to satellites

DISADVANTAGES 1.

2.

3.

4.

Capital cost is very high Large area of land is required Large number of solar panels are required Affected by seasons.

WIND ENERGY ADVANTAGES 1. Wind is Renewable and free of cost 2. Pollution free 3. Can be installed in remote villages, thus reducing costly transmission lines DISADVANTAGES 1. Capital cost is very high 2. Large area of land is required 3. Maintenance cost is very high

TIDAL ENERGY ADVANTAGES 1. It is inexhaustible source of energy 2. No problem of pollution 3. The cost of power generation is quite low 115

4. High output can be obtained compared to solar or wind energy DISADVANTAGES 1.

2.

3.

4.

Capital cost is very high As the head is not constant, variable output is obtained As the head is low, large amount of water is necessary for the turbine It will not operate when the available head is less than 0.5m

GEOTHERMAL ENERGY ADVANTAGES 1.

2.

3.

4.

Geothermal energy is cheaper Used as space heating for buildings Used as industrial process heat Geothermal energy is inexhaustible

DISADVANTAGES 1. Low overall power production efficiency (about 15%) 2. Large areas are needed foe exploitation of geothermal energy

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References: 1) Hall, D.O. and House, J.I., Biomass and Bioenergy, 6,11-30 (1994).

2) Miyamoto, K., In "Recombinant Microbes for Industrial and Agricultural Applications" Eds. Murooka, Y. and Imanaka, T., 771-785 (1994) Marcel Dekker, Inc., New York, Basel, Hong Kong.

3) Borowitzka, M.A., In "Micro-algal biotechnology" Eds. Borowitzka, M.A. and Borowitzka, L.J., 257-287 (1988) Cambridge University Press, Cambridge.

4) Background. Marine Current Turbines Ltd. 22 Apr. 2005. <http://www.marineturbines.com/ background.htm> 5) Clark, Peter, Klossner, Rebecca, and Kologe, Lauren. “Tidal Energy”. 13 Nov 2003. 22 Apr. 2005. <http://www.ems.psu.edu/~elsworth/courses/cause2003/finalprojects/ canutepaper.pdf> 6) Information Resources: Ocean Energy. 26 Apr. 2005. U.S. Department of Energy. 22 Apr. 2005 <http:// www.eere.energy.gov/consumerinfo/factsheets/nb1.html> 7) Johnson, Jeff. “Power From Moving Water”. C&EN.82.40. 4 Oct. 2004. <http://pubs.acs.org/ cen/coverstory/8240/ print/8240energy.html> 8) Jones, Anthony T. “Renewable ocean energy systems becoming more viable.” Financial Times: Energy. 20 Apr. 2001.

9) Kennedy, President John F. as read into Congressional Record, by Hon. Thomas J. Dodd; as reported in Congressional Record – Appendix; October 22, 1963; pp 6580-6581 [Proceedings and Debates of the 88th Congress, First Session] 10) Marine Energy – Wave Power. 5 May 2005. Argyll & the Islands Enterprise. 22 Apr. 2005 <http://www.hie.co.uk/ aie/wave_power.html> 11) Marine Energy – Tidal Power. 5 May 2005. Argyll & the Islands Enterprise. 22 Apr. 2005 <http://www.hie.co.uk/ aie/tidal_power.html> 12) Ocean Topics. 26 Apr. 2005. U.S. Department of Energy. 22 Apr. 2005 <http://www.eere.energy.gov/RE/ ocean.html> 13) OWEC – Offshore Wave Energy Converters. 8 Jan. 2002. Interproject Service. 22 Apr. 2005 <http:// members.tripod.com/Interproject/presentation.htm> 14) Prototype Project. Wave Dragon. 22 Apr. 2005 <http://www.wavedragon.net/technology/ prototype.htm> 15) Ross, David. Power From the Waves. New York: Oxford University Press Inc., 1995.

16) Technology. Marine Current Turbines Ltd. 22 Apr. 2005. <http://www.marineturbines.com/ technical.htm> 17) Wave Energy: A Concentrated Form of Solar Energy. Wave Dragon. 22 Apr. 2005 <http://www.wavedragon.net/ technology/wave-energy.htm> 18) Wave Energy Overview – The Market. ATLAS. 22 Apr. 2005 <http://europa.eu.int/comm/ energy_transport/atlas/ htmlu/wavomark.html> 19) 20) 21) 22)

HTTP://WWW.ESTIF.ORG/ST_ENERGY/TECHNOLOGY/SOLAR_HC_MAP/ http://www.mpoweruk.com/wind_power.htm http://www.altenergy.org/renewables/solar/latest-solar-technology.html http://www.livemint.com/Industry/lGM9f97bTxoboIZebYtq9N/10-technologies-shaping-thefuture-of-solar-power.html 23) www.sbp.de 24) http://www.mpoweruk.com/wind_power.htm 117

25) http://www.alternative-energy-news.info/solar-wind-power/ Sites: http://home.clara.net/darvill/altenerg/tidal.htm Tidal Energy Images at: http://www.mywindpowersystem.com/wp-content/uploads/2009/08/renewable-energy-tidal-2.gif 1) http://www.energybc.ca/profiles/runofriver.html (last access: 08.10.2016) 2) http://www.thefreedictionary.com/Hydroelectric+energy (last access: 08.10.2016) 3) http://www.wasserkraft.info/de/warum-wasserkraft.html (last access: 08.10.2016) 4) http://www.erneuerbareenergien.de/EE/Navigation/DE/Technologien/Wasserkraft/wasserkraft.html (last access: 08.10.2016) 5) http://energie-strom.com/erneuerbare_energien/wasserkraft/laufwasserkraftwerk.html (last access: 08.10.2016) 6) http://energiespeicher.blogspot.de/2012/04/wirkungsgrad-von-speichern_17.html (last access: 08.10.2016)

http://igutek.scripts.mit.edu/terrascope/tidal-energy-farm.jpg

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